• Structural Engineering and Mechanics
• /
• 제60권3호
• /
• pp.489-505
• /
• 2016

Sinusoidal shear deformation theory (SSDT) is developed here for dynamic buckling of functionally graded (FG) nano-plates. The material properties of plate are assumed to vary according to power law distribution of the volume fraction of the constituents. In order to present a realistic model, the structural damping of nano-structure is considered using Kelvin-Voigt model. The surrounding elastic medium is modeled with a novel foundation namely as orthotropic visco-Pasternak medium. Size effects are incorporated based on Eringen'n nonlocal theory. Equations of motion are derived from the Hamilton's principle. The differential quadrature method (DQM) in conjunction with Bolotin method is applied for obtaining the dynamic instability region (DIR). The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, orthotropic visco-Pasternak foundation, power index of FG plate, structural damping and boundary conditions on the dynamic instability of system. The results are compared with those of first order shear deformation theory and higher-order shear deformation theory. It can be concluded that the proposed theory is accurate and efficient in predicting the dynamic buckling responses of system.

• 한국생활과학회지
• /
• 제14권5호
• /
• pp.821-832
• /
• 2005

The purpose of this study is to investigate bathing habits and behaviors, and to find out consumers' needs for washcloth, which in this case refers to Korean exfoliating cloth for bathing purpose. Subjects of this study were females of 20s to 50s living in urban area. Four hundred and twenty-six (426) women were interviewed with a structured questionnaire. Data were analyzed by ANOVA, factor analysis, correlation analysis, MDS. The results of this study are briefly summarized as follows: The most popular bathing type was shower (84.9%). Personal hygiene was one of the commonest purpose of bathing, and other purposes included health maintenance, stress alleviation, and beauty in order. Dimensions of consumer needs for washcloth were extracted from factor analysis as following properties: tactile, tough, aesthetic, constructive, and hygienic. The preference for washcloth type was related to skin type. "Non-skin damage property" was the most important parameter to choose washcloth and the other parameters included massage effect, tactile property, foaming property, and easy-to-use property.

• 한국경영과학회지
• /
• 제23권4호
• /
• pp.111-130
• /
• 1998

We propose an imperfect repair model which depends on external effects quantified by covariates. The model is based on the Brown-Proschan imperfect repair model wherefrom the probability of perfect repair is represented by a function of covariates. We are motivated by deficiency of the BP model whose stationarity prevents us from predicting dynamically the time to next failure according to external condition. Five types of function for the probability of perfect repair are proposed. This article also presents a procedure for estimating the parameter of the function for the probability of perfect repair, as well as the inherent lifetime distribution of the system, based on consecutive inter-failure times and the covariates. The estimation procedure is based on the expectation-maximization principle which is suitable to incomplete data problems. focusing on the maximization step, we derive some theorems which guarantee the existence of the solution. A Monte Carlo study is also performed to illustrate the prediction power of the model as well as to show reasonable properties of the estimates. The model reduces significantly the mean square error of the in-sample prediction. so it can be utilized in real fields for evaluating and maintaining repairable systems.

• 터널과지하공간
• /
• 제22권1호
• /
• pp.60-68
• /
• 2012

본 연구에서는 도로터널을 대상으로 최소 이격거리가 0.5D 이하인 근접 병설터널의 암반 필라 거동을 3차원 수치해석방법으로 검토하였다. 암반 필라의 거동에 영향을 미치는 매개변수로 이격거리와 심도(토피고) 및 암반조건의 변화에 따른 안전율을 평가하였다. 이격거리가 증가할수록 토피고와 암반조건에 따른 안전율 추세곡선은 비선형 거동을 보여 주었으며, 최소 안전율을 기준으로 최소 이격거리를 산정하여 설계도표를 제시하였다.

• 설비공학논문집
• /
• 제30권2호
• /
• pp.92-99
• /
• 2018

A numerical analysis of a compressor dehumidifier has been conducted focusing on the air side heat transfer, which is a part of a series research on the dehumidifier. The moving reference frame was applied to the fan modeling, and the porous model was used for the evaporator and condenser modeling. Curve fitting obtained the inertial and viscous resistances parameters to the results of the physical model of the unit cell with actual shape of a fin tube. The porous model was validated within a reasonable computation time for the range of practical inlet velocity of a dehumidifier. A parametric study has been conducted for fin number, fan speed (i.e., air flow rate), and evaporator/condenser tube arrangement. ANOVA analysis showed the dependency of each parameter on the velocity and temperature uniformity, which are desirable for high performance of the dehumidifier.

• 대한후두음성언어의학회지
• /
• 제9권2호
• /
• pp.134-141
• /
• 1998

Mutational falsetto is a kind of voice disorders due to the failure to acquire proper low-pitched voice during the puberty. The patients with mutational falsetto can produce the normal low-pitched voice by the surgical treatment, like the type III-thyroplasty, or the voice therapy. The present study is, focusing on the latter treatment, to consider the efficiency of voice therapy for the mutational falsetto. The 7 patients who were diagnosed as mutational falsetto by the laryngologists, and treated by the voice therapist were selected as subjects. Their voices of pretherapy and posttherapy were analyzed on the aspects of acoustics and aerodynamics. Acoustic analysis was done by the MDVP(Multidimensional Voice Program) of CSL(Computerized Speech Lab, Kay Elemetrics, Co.), and aerodynamic analysis, by the Maximum Sustained Phonation of Aerophone II(Kay Elemetrics, Co.). By these measurements, we could find that fundamental frequency(F0) was significantly lowered, on the average, 65Hz. Maximum phonation time(MPT) was increased 4.57 second, and shimmer was decreased 1.644%, respectively, and each changes was statistically significant, too. On the average, jitter was decreased 0.499%, mean flow rate(MFR) was decreased 27.71ml/sec, and NHR was increased 0.023 which was the only parameter not showing improvement. But the changes of jitter, MFR and NHR were not statistically significant.

• Steel and Composite Structures
• /
• 제28권6호
• /
• pp.749-758
• /
• 2018

Free axial vibration of axially functionally graded (AFG) nanorods is studied by focusing on the inertia of lateral motions and shear stiffness effects. To this end, Bishop's theory considering the inertia of the lateral motions and shear stiffness effects and the nonlocal theory considering the small scale effect are used. The material properties are assumed to change continuously through the length of the AFG nanorod according to a power-law distribution. Then, nonlocal governing equation of motion and boundary conditions are derived by implementing the Hamilton's principle. The governing equation is solved using the harmonic differential quadrature method (HDQM), After that, the first five axial natural frequencies of the AFG nanorod with clamped-clamped end condition are obtained. In the next step, effects of various parameters like the length of the AFG nanorod, the diameter of the AFG nanorod, material properties, and the nonlocal parameter value on natural frequencies are investigated. Results of the present study can be useful in more accurate design of nano-electro-mechanical systems in which nanotubes are used.

• 한국레이저가공학회지
• /
• 제2권3호
• /
• pp.11-18
• /
• 1999

This paper describes the weldability of carbon steel and stainless steel using 5㎾ $CO_2$ laser system with nearly multi-mode beam and a parabolic focusing mirror. In the laser welding of steels, major welding parameters are focal point, travel speed, beam power, shield gas and gap tolerance, etc.. Two kinds of gases(Ar, He) were used as a assist gas and supplied through the external nozzle. It is very important for optimum condition to remove plasma plume which absorbs laser beam and to obtain deep penetration and sound weld bead. Bead-on-plate welding tests were carried out for the experiments. Penetration data were obtained with various welding parameters and the effects of welding parameters were discussed. Butt welding tests were performed with various conditions. Only the optimum laser parameters assured good weld quality As a result of this study, We achieve the fundamental weldabilities using a high power $CO_2$ laser for carbon steel and stainless steel.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.2-5
• /
• 2008

This study describes the numerical simulation of three-dimensional droplet formation and the following motion in a cross-junction microchannel by using the Lattice Boltzmann Method (LBM). Our aim is to develop the three-dimensional binary fluids model, consisting of two sets of distribution functions to represent the total fluid density and the density difference, which introduces the repulsive interaction consistent with a free-energy function between two fluids. We validated the LBM code with the velocity profile in a 3-dimensional rectangular channel. Then, we applied our code to the numerical simulation of a binary fluid flow in a cross-junction channel focusing on the investigation of the droplet formulation. Due to the pressure and interfacial-tension effect, one component of the fluids which is injected from one inlet is cut off into many droplets periodically by the other component which is injected from the other inlets. We considered the effect of the boundary conditions for density difference (order parameter) on the wetting of the droplet to the side walls.

• 한국생활과학회지
• /
• 제18권3호
• /
• pp.749-756
• /
• 2009

Keeping abreast with the latest consumer's trends, industries are focusing on sensibility aspects of products to meet consumer's needs. The car(?) seat cover fabrics are more closely related to human senses than anything else. This study attempted to investigate which seat cover fabric can give good feeling to consumers and to analyze their characteristics. Twelve kinds of jacquard fabric used for seat cover were selected. The Kawabata Evaluation System was used to measure the mechanical properties of 12 jacquard fabrics, and tactile sensibility(TS), and preference(P) determined by subjective evaluation of 160 participants were also utilized. The stepwise regression analysis was made to select the most significant mechanical properties, and some models for predicting tactile sensibility and preference was developed. The results are briefly summarized as follows: the most important parameter to choose seat cover fabric is a "hygienic property" and the other parameters are 'materials with color fastness', 'compressive property', 'color', 'antibacterial property', 'easy-care property'. The LogSMD, LogB, LC, EM were selected as significant mechanical properties affecting tactile sensibility. Also, the LC, LogB, LogSMD, LogWC, LogMMD were selected as significant mechanical properties affecting preference.