• Journal of Korea Game Society
• /
• v.15 no.5
• /
• pp.143-152
• /
• 2015

Unlike simulating general 'particle-based fluid explosion', simulating fluid with elasticity requires various experimental methods in order to show the realistic deformation of the matter. The existing studies on particle-based viscoelastic fluid only focused on matters' plastic deformation which can be found in mud or paint, based on the maximum distortion energy theory and maximum shear stress theory. However, these former researches could not simulate the brittle deformation which can be seen from silicon or highly elastic rubber when great external forces above limits are applied. This study suggests a brittle simulation method based on the Coulomb-Mohr theory, the idea that a yield occurs when maximum stress on a matter reaches to its rupture stress. This theory has a significant difference from the existing particle-based simulations which measures the forces on a matter by length or volume. Using a strong-elastic semifluid which Coulomb-Mohr theory is applied, realistic deformation process of a matter was observed as its forced surface reached to the rupture stress. When semifluid hit the ground, the impact of deformation can be explained by using Coulomb-Mohr theory.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.04a
• /
• pp.153-158
• /
• 1995

보 및 평판의 진동에 대해서 에너지의 손실은 재료감쇠를 이용한 표면감쇠처리나 지지부에서의 감쇠처리에 의하여 증가될 수 있다. 감쇠재료를 이용한 표면감쇠처리의 예로서 보/평판 표면에 접착되는 감쇠 테이프나 코팅등은 아주 효과적임이 입증되었다. 마찬가지로 지지부 감쇠처리는 점탄성재료의 삽입에 의해서 설명될수 있다[1]. 보/평판의 감쇠에 대한 최근의 많은 연구들은 진동하고 있는 보/평판의 표면에 적용하는 감쇠 테이프 혹은 적층형태의 감쇠 처리방법에 대해서 주로 수행되었다. 일반적으로 표면감쇠처리방법은 진동감소에 아주 효과적이지만 실제 적용상에서 항상 가능한 것은 아니며, 이와 같은 경웨는 지지부 감쇠 처리방법에 의존하게 된다[2]. 감쇠특성을 갖는 점탄성재료를 실제로 적용할 때 보/평판의 유한한 길이가 점탄성재료로 지지되며 점탄성재료의 물성치와 치수에 따라서 계의 모우드 매개변수(고유진동수, 계의 손실계수 그리고 모우드형상)가 크게 달라진다. 그리고 이와 같은 계에 대해서는 지지부의 거동보다는 전체 시스템의 고유진동수와 손실계수 그리고 보 영역에서의 모우드 형상에 더 관심이 있으므로 지지부 영역을 집중매개변수(lumped parameter)로 나타내어 계를 해석할 수 있다. 일반적으로 보와 평판의 경계에서는 병진 및 회전방향의 강성 뿐만 아니라 두 강성사이에 연성효과도 동시에 발생하게 되므로 이 항을 고려하여 계를 모델링해야 한다. 본 연구에서는 우선 점탄성 재료에 의한 지지부영역의 등가 강성계수들을 구하고 경계에 강성행렬을 갖는 보의 등가시스템을 얻는다. 그리고 등가시스템의 주파수방정식으로부터 모우드 매개변수에 대한 지지부의 영향을 살펴본다. 또한 시스템이 비교적 복잡한 사각 평판의 진동에 대해서도 동강성행렬법(dynamic stiffness matrix method)을 이용하여 해석하고자 한다. 수준임이 입증되었다. 본 연구의 결과를 토대로우리나라 젊고 건강한 남성에게 적합한 무게상수는 작업자군에 대하여 25.05kg, 학생군에 대하여 20.24kg 으로 나타나 이는 미국 NIOSH 안전기준과 대체로 일치함을 발견하였다.ive structures utilized in Client/server architecture for distribution and cooperative processing of application between server and client this study presents two different data management methods under the Client/server environment; one is "Remote Data Management Method" which uses file server or database server and. the other is "Distributed Data Management Method" using distributed database management system. The result of this study leads to the conclusion that in the client/server environment although distributed application is assumed, the data could become centralized (in the case of file server or database server) or decentralized (in the case of distributed database system) and the data management method through a distributed database system where complete responsi

• Journal of the Korean Geotechnical Society
• /
• v.19 no.4
• /
• pp.145-153
• /
• 2003

The resonant column testing determines the shear modulus and material damping factor dependent on the shear strain magnitude, based on the wave-propagation theory. The determination of the dynamic soil properties requires the theoretical formulation of the dynamic behavior of the resonant column testing system. One of the theoretical formulations is the use of the wave equation for the soil specimen in the resonant column testing device. Wood, Richart and Hall derived the wave equation by assuming the linear elastic soil, and didn't take the material damping into consideration. Hardin incorporated the viscoelastic damping of soil in the wave equation, but he had to assume the material damping factor for the determination of the shear modulus. For the better theoretical formulation of the resonant column testing, this study derived a new wave equation to include the viscosity of soil, and proposed an approach for the solution. Also, in this study, the equation of motion for the testing system, which is another approach of the theoretical formulation of the resonant column testing, was also derived. The equation of motion leads to the better understanding of the resonant column testing, which includes the dynamic magnification factor and the phase angle of the response. For the verification of the proposed equation of motion for the resonant column testing, the finite element analysis was performed for the resonant column testing. The comparison of the dynamic magnification factors and the phase angles far the system response were performed.

• International Journal of Highway Engineering
• /
• v.3 no.2 s.8
• /
• pp.113-121
• /
• 2001

Among the currently available binder specifications, Superpave Performance Grade asphalt specification is regarded as a superior specification on its theoretical background as well as pavement performance relationship. Many difficulties are expected; however, for Superpave implementation in Korea because of heavy burden of equipment cost as well as lack of trained personnel in asphalt industry, which may too much barrier to overcome in Korean situation. As an effort to improve qualify of asphalt binder, recently, people discuss about a possibility of constituting a performance-based asphalt specification using rather easy-to-measure asphalt properties. The objective of this paper is to determine the possibility of constituting a performance-based asphalt specification using an empirical asphalt properties, such as penetration ring and ball softening point rather than using fundamental properties of asphalt. Nine straight asphalts, that covers entire straight asphalt from all Korean refineries, and eighteen modified asphalts that were modified from two modifiers were included in the study. An analysis was made through a comparison between empirical properties and Superpave PG criteria. This study concluded that it may possible to constitute a pseudo-Superpave-like specification using an empirical asphalt properties as a specification criteria. Therefore, more systematic research is needed to constitute the asphalt specification.

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.29 no.1
• /
• pp.73-83
• /
• 1997

Most of the materials used in various industrial fields and also in our daily life are multi-component materials or composite materials, and it is well known that there are many cases where adhesion between the constituents within the bonded systems plays an important role. There are various types of performance evaluation tests for the bonded materials, among which tests for evaluating the bond performance under various conditions may be regarded as the most interesting ones for those engaged in work related to adhesion. I have studied on the mechanism of adhesion form the rheological standpoint with my colleagues, including some students from Korea, and I am very happy to be able to have a talk on some of our research works. In Japan, the so-called "adhesives" are usually classified into two categories;adhesives and pressure sensitive adhesives (PSA). Adhesives are the materials which solidify after bonding and are after used as the structural adhesives because the adhesive strength is comparatively strong. On the other hand, the pressure sensitive adhesives never solidify and are used as PSA tapes, labels or decals. About the adhesives, we have examined the dependence of adhesive strength(shear, tensile, peel) upon both temperature and rate of deformation, and found out some empirical rules which are applicable to most of the adhesive systems. We have also developed a simplified theory of adhesion, which is deseribed in terms of mechanical equivalent mode1 and a few failure criteria. Although some of the common rules can be accounted for according to this theory, it must be pointed out that a fracture mechanical approach ms inevitable especially in the region where the meehanical relaxation time of the adhesive is extremely large [W. W. Lim and H. Mizumachi]. About the pressure sensitive adhesives, we have studied on the PSA performance (peel, tack, holding power) as a function of both the viscoelastic properties and surface chemical properties of the materials, and found out some rules, and again we have developed a theory which deseribes the mechanism. And in addition, we have studied on the miscibility between linear polymers and oligomers, because PSA is generally manufactured by blending gums and tackifier resins. Many phase diagrams have been found and some of them have been analyzed on thermodynamic basis, and it became evident that the miscibility is a very important factor in PSA [H. J. Kin and H. Mizumachi]. In this presentation, I want to emphasize the fact that the adhesion performance is closely related to the structure/property of the adhesives.adhesives.

• Journal of the Korean Wood Science and Technology
• /
• v.48 no.4
• /
• pp.431-449
• /
• 2020

Structural property of most hydrogels is soft, resulting in low mechanical performance that limits their usage in the biomedical applications. For overcoming the drawback, cellulose nanocrystals (CNCs) were adopted in this study. Effects of CNCs on characteristics and drug delivery performance of poly (vinyl alcohol) based hydrogels were explored. FT-IR results showed that the fabricated hydrogels had semi-IPN (semi-interpenetrating polymer network) by formation of acetal and aldehyde bridge. Water absorption and swelling ratio decreased with increasing CNCs content, and the hydrogels with CNCs showed better viscoelastic performance than the without CNCs. Also, CNCs mostly improved the ability of the hydrogel to absorb the drug and the sustainability of the drug release. These results demonstrated that incorporating CNCs into the hydrogel systems can be a good alternative to improve drug delivery performance and mechanical property of the hydrogels.

• Applied Biological Chemistry
• /
• v.40 no.6
• /
• pp.525-530
• /
• 1997

The changes in rheological properties of egg white stored in biodegradable package were investigated by pH change, failure stress and stress relaxation curve, and compared with control without package and complex PE. Initial pH of egg white stored in biodegradable package changed from 8.39 to 9.3 after 8 day storage, showing similar trend in pH change as that of control without package. Initial 14.25 N failure stress was changed into 6.76 N in biodegradable package and 9.31 N in control. Complex PE, having a relatively low gas permeability compared to biodegradable package, showed less pH changes from 8.30 to 8.81, but a greater decrease in failure stress into 5.29 N, indicating more deteriorating effect in complex PE package. Viscoelastic constants, such as elastic constant and viscous constant, obtained from stress-relaxation curve by three element Maxwell model were not significantly different between control and biodegradable package, but eggs stored in complex PE showed greater changes during storage. Therefore, the permeability seems to be the major factors to influence the rheological properties of egg and biodegradable packaging materials showed a potential substitute package for eggs.

• Korean Journal of Food Science and Technology
• /
• v.44 no.2
• /
• pp.216-223
• /
• 2012

Dextran was produced by $Leuconostoc$ $mesenteroides$ SM with various contents of yeast extract and its rheological properties were modulated, via an addition of hydroxypropyl methylcellulose (HPMC) of different viscosities. The conversion yield reached 90% after adding 3% yeast extract, which remained constant, thereafter. The acidity of the cultures was approximately 1.4 and 0.9% after fermentation for 24 h at 25 and $30^{\circ}C$, respectively. The total dextran content (107.3 g/kg) was the highest in the presence of the 3% yeast extract. Under the same conditions, the consistency, viscous modulus (G"), and elastic modulus (G') of the cultures were $37.6\;Pa{\cdot}s^n$, 38 Pa, and 50 Pa, respectively. The rheological properties of the culture were changed drastically by the fortification with HPMC of higher concentration and viscosity. The addition of 10% HPMC (4,000 cp) resulted in a significant increase in G" to 1,950 Pa. Furthermore, adding HPMC to a viscous culture resulted in a remarkable increase in both hardness and firmness.

• Korean Journal of Food Science and Technology
• /
• v.45 no.4
• /
• pp.434-440
• /
• 2013

Functional properties of Cheonnyuncho fruit paste (CFP) were enhanced by fermentation, using Leuconostoc mesenteroides SM. The stability of CFP pigment was maintained and microorganisms in crude CFP were sterilized by heating at $80^{\circ}C$ for 30 min. The production of dextran in CFP was increased by increasing the fermentation time and sugar content, resulting in an increase of consistency. The CFP fermented with 20% sucrose contained 4.8% mucilage after fermentation for 2 days. In particular, the production of mucilage was greatly enhanced by fortification with 3% sodium citrate in CFP, resulting in mucilage production of 7%. In addition, the viscous modulus of fermented CFP showed a greater increase than that of the elastic modulus. Thus, it was concluded that CFP fermented by L. mesenteroides SM can be fortified with functional ingredients, such as mucilage and probiotics, with enhanced rheological properties. Therefore fermented CFP can be utilized as the functional ingredients for functional foods.

• Proceedings of the KACD Conference
• /
• 2008.05a
• /
• pp.235-245
• /
• 2008

The aim of this study was to develop a method for measuring the slumping resistance of resin composites and to relate it to the rheological characteristics. Five commercial hybrid composites (Z100. Z250. DenFil, Tetric Ceram. ClearFil) and a nanofill composite (Z350) were used to make disc-shaped specimens of 2 mm thickness. An aluminum mold with square shaped cutting surface was pressed onto the composite discs to make standardized imprints. The imprints were light-cured either immediately (non-slumped) or after waiting for 3 minutes at $25^{\circ}C$ (slumped). White stone replicas were made and then scanned for topography using a laser 3-D profilometer. Slumping resistance index (SRI) was defined as the ratio of the groove depth of the slumped specimen to that of the non-slumped specimen. The pre-cure viscoelasticity of each composite was evaluated by an oscillatory shear test and normal stress was measured by a squeeze test using a rheometer. Flow test was also performed using a flow tester. Correlation analysis was performed to investigate the relationship between the viscoelastic properties and the SRI. SRI varied between the six materials (Z100 < DenFil < Z250 < ClearFil < Tetric Ceram < Z350). The SRI was strongly correlated with the viscous (loss) shear modulus G' but not with the loss tangent. Also. slumping resistance was more closely related to the resistance to shear flow than to the normal stress. Slumping tendency could be quantified using the imprint method and SRI. The index may be applicable to evaluate the clinical handling characteristics of composites.