• Structural Engineering and Mechanics
• /
• v.92 no.3
• /
• pp.227-243
• /
• 2024

This paper introduces a methodology that combines Multivariate Adaptive Regression Splines (MARS) modelling and Monte Carlo Simulation to investigate the natural frequencies of porous functionally graded material (FGM) plates along with the frequency response function (FRF) analysis. The MARS model captures the nonlinear relationship between natural frequencies and different parameters, while the FRF approach provides insights into the plate's frequency response. The proposed methodology is accurate and helpful in studying the impact of porosity, power law index, temperature, and plate thickness on the first three natural frequencies, considering the stochastic variations in material properties caused by manufacturing errors. The porous FGM plate is subjected to a traditional finite element (FE) analysis with random material properties. The power law distribution is used to ascertain the material characteristics of porous functionally graded plates. The effects of critical material characteristics, such as elastic Young's modulus, shear modulus, Poisson's ratio, and mass density, on the natural frequencies of porous FGM are examined. The results show that MARS-based finite element analysis has better computational efficiency than Monte Carlo simulations-based finite element analysis.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.spc8
• /
• pp.2899-2905
• /
• 2011

We have demonstrated that TPyPA can be used as an efficient multi-functional material for OLEDs; hole transporting material (HTL), blue and white-light emitter. The device based on TPyPA as the HTL exhibited an external quantum efficiency of 1.7% and a luminance efficiency of 4.2 cd/A; these values are 40% higher than the external quantum efficiency and luminance efficiency of the NPD-based reference device. The device based on TPyPA as a blue-light emitter exhibited an external quantum efficiency of 4.2% and a luminance efficiency of 5.3 $cdA^{-1}$ with CIE coordinates at (0.16, 0.14), the device based on TPyPA as a white-light emitter exhibited an external quantum efficiency of 3.2% and a luminance efficiency of 7.7 $cdA^{-1}$ with CIE coordinates at (0.33, 0.39). Also, TPyPA-based organic solar cell (OSC) exhibited a maximum power conversion efficiency of 0.35%. TPyPA-based organic thin-film transistors (OTFTs) exhibited highly efficient field-effect mobility (${\mu}_{FET}$) of $1.7{\times}10^{-4}cm^2V^{-1}s^{-1}$, a threshold voltage ($V_{th}$) of -15.9 V, and an on/off current ratio of $8.6{\times}10^3$.

• Journal of Korean Society of Rural Planning
• /
• v.3 no.2
• /
• pp.81-89
• /
• 1997

Still today, many streams are channelized and embanked in Korea. On the other hand, some urban streams are being restored to their natural shapes by landscape planners. It would be better to improve rural streams in a way that would not require restoration in later days. Then, one important question is what kind of embankments the residents prefer for what reasons. Five simulated photos showing from very natural to artificial embankments were used in surveying 90 residents of three villages. Major findings are ; 1. Residents regard safety(from flooding) is the most critical factor to be considered in selection of stream bank materials. 2. They think ideal materials are natural stones or concrete blocks as they look tidy. Concrete retaining walls or vegetated natural slopes are not regarded good. 3. The most preferred material is concrete retaining wall, and the least preferred is vegetated natural slope. They prefer concrete retaining wall which they do not think an ideal material, because it will make a safe bank. 4. Natural stone bank is most preferred for its apperance, and vegetated natural slpoe is most disliked as it may collapse and as it does not look clean.

• Journal of the Korea Institute of Building Construction
• /
• v.11 no.6
• /
• pp.557-566
• /
• 2011

The surfactants facilitate the formation of foam bubbles under a proper condition and provide stability of foam bubbles by decreasing the surface tension of solutions and increasing the viscosity of foam surface. However, there have been almost no practical data of foam concrete in this regard so far. This study aims to understand the effects of foaming agents such as anionic synthetic surfactant and anionic natural material surfactant on the low density foamed concrete. From the experiment, the vegetable soap of anionic natural material surfactants showed a higher foaming rate, more open pores, slightly lower compressive strength, and a higher permeability coefficient compared to the vegetable soap of anionic synthetic surfactants. It is believed that the natural material surfactants make not only the surface tension of the solution low but also the viscosity of slurry high.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2006.11a
• /
• pp.43-46
• /
• 2006

The Hwangtoh is one of the traditional construction material used in wall, plastering material, and ondol (Korean underfloor heating system) with stone and wood. It is an important greenness material and it has much advantages such as; high storage of heat, auto-purification, antibiotic ability, and emission of far infrared rays. But, it is not developed and not used in modern construction because of its low strength and properties of dry shrinkage crack. According to the recent researches and studies, it is evaluated for natural pozzolanic material like flyash or pozzolan. It's possibility on construction material is high because it's chemical and mineralogical proportion is like as Metakaolin and Kaolinite. In this point of view, this study aims to analyze the physical properties on Hwangtoh mortar through an experiment with various activation condition of Hwangtoh, which is natural pozzolanic material, for the purpose of increase the using possibility in construction material.

• Proceedings of the Korean Society of Dyers and Finishers Conference
• /
• 2012.03a
• /
• pp.101-101
• /
• 2012

천연가죽에 색상을 부여하기 위한 염색공정에서 종전의 합성염료가 아닌 자연에서 추출한 천연염료를 이용하여 블루색상을 가지는 피혁 제조 공정을 확립하였다. 피혁에 적용 가능한 블루색상을 가지는 천연염료 중에 쪽 염료가 유일한 상황이다. 가죽 무게 대비 5%의 쪽염료를 가죽 제조 드럼에 투입하여 100분간 충분히 회전시킨 후에 가죽의 유연성을 부여하는 가지제를 12% 추가로 투입하여 블루 색상을 가지는 가죽을 제조하였다. 그 결과 마찰견뢰도, 일광견뢰도, K/S가 우수한 피혁 염색공정을 확립하였다.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.18 no.12
• /
• pp.28-37
• /
• 2019

Due to their flexible tailoring qualities, composites have become fascinating materials for structural engineers. While the research area of fiber-reinforced composite materials was previously limited to synthetic materials, natural fibers have recently become the primary research focus as the best alternative to artificial fibers. The natural fibers are eco-friendly and relatively cheaper than synthetic fibers. The main concern of current research into natural fiber-reinforced composites is the prediction and enhancement of the effective material properties. In the present work, finite element analysis is used with a numerical homogenization approach to determine the effective material properties of jute fiber-reinforced epoxy composites with various volume fractions of fiber. The finite element analysis results for the jute fiber-reinforced epoxy composite are then compared with several well-known analytical models.

• Structural Engineering and Mechanics
• /
• v.57 no.2
• /
• pp.239-263
• /
• 2016

The paper studies the natural oscillation of the three-layered solid sphere with a middle layer made of Functionally Graded Material (FGM). It is assumed that the materials of the core and outer layer of the sphere are homogeneous and isotropic elastic. The three-dimensional exact equations and relations of linear elastodynamics are employed for the investigations. The discrete-analytical method proposed by the first author in his earlier works is applied for solution of the corresponding eigenvalue problem. It is assumed that the modulus of elasticity, Poisson's ratio and density of the middle-layer material vary continuously through the inward radial direction according to power law distribution. Numerical results on the natural frequencies related to the torsional and spheroidal oscillation modes are presented and discussed. In particular, it is established that the increase of the modulus of elasticity (mass density) in the inward radial direction causes an increase (a decrease) in the values of the natural frequencies.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.10a
• /
• pp.923-924
• /
• 2012

• Macromolecular Research
• /
• v.15 no.2
• /
• pp.191-194
• /
• 2007