• Advances in concrete construction
• /
• 제6권6호
• /
• pp.585-610
• /
• 2018

In this study, vibration analysis of a concrete foundation-reinforced by $SiO_2$ nanoparticles resting on soil bed is investigated. The soil medium is simulated with spring constants. Furthermore, the Mori-Tanaka low is used for obtaining the material properties of nano-composite structure and considering agglomeration effects. Using third order shear deformation theory or Reddy theory, the total potential energy of system is calculated and by means of the Hamilton's principle, the coupled motion equations are obtained. Also, based an analytical method, the frequency of system is calculated. The effects of volume percent and agglomeration of $SiO_2$ nanoparticles, soil medium and geometrical parameters of structure are shown on the frequency of system. Results show that with increasing the volume percent of $SiO_2$ nanoparticles, the frequency of structure is increased.

• Structural Engineering and Mechanics
• /
• 제69권5호
• /
• pp.547-555
• /
• 2019

In this study, vibration analysis of a concrete foundation-reinforced by $SiO_2$ nanoparticles resting on soil bed is investigated. The soil medium is simulated with spring constants. Furthermore, the Mori-Tanaka low is used for obtaining the material properties of nano-composite structure and considering agglomeration effects. Using third order shear deformation theory or Reddy theory, the total potential energy of system is calculated and by means of the Hamilton's principle, the coupled motion equations are obtained. Also, based an analytical method, the frequency of system is calculated. The effects of volume percent and agglomeration of $SiO_2$ nanoparticles, soil medium and geometrical parameters of structure are shown on the frequency of system. Results show that with increasing the volume percent of $SiO_2$ nanoparticles, the frequency of structure is increased.

• Computers and Concrete
• /
• 제21권1호
• /
• pp.31-37
• /
• 2018

This paper deals with the stability analysis of concrete pipes mixed with nanoparticles conveying fluid. Instead of cement, the $Fe_2O_3$ nanoparticles are used in construction of the concrete pipe. The Navier-Stokes equations are used for obtaining the radial force of the fluid. Mori-Tanaka model is used for calculating the effective material properties of the concrete $pipe-Fe_2O_3$ nanoparticles considering the agglomeration of the nanoparticles. The first order shear deformation theory (FSDT) is used for mathematical modeling of the structure. The motion equations are derived based on energy method and Hamilton's principal. An exact solution is used for stability analysis of the structure. The effects of fluid, volume percent and agglomeration of $Fe_2O_3$ nanoparticles, magnetic field and geometrical parameters of pipe are shown on the stability behaviour of system. Results show that considering the agglomeration of $Fe_2O_3$ nanoparticles, the critical fluid velocity of the concrete pipe is decreased.

• Steel and Composite Structures
• /
• 제32권6호
• /
• pp.795-806
• /
• 2019

In this paper, free vibration of sandwich beam with flexible core resting on orthotropic Pasternak is investigated. The top and bottom layers are reinforced by carbon nanotubes (CNTs). This sandwich structural is modeled by Euler and Frostig theories. The effect of agglomeration using Mori-Tanaka model is considered. The Eringen's theory is applied for size effect. The structural damping is investigated by Kelvin-voigt model. The motion equations are calculated by Hamilton's principle and energy method. Using analytical method, the frequency of the structure is obtained. The effect of agglomeration and CNTs volume percent for different parameter such as damping of structure, thickens and spring constant of elastic medium are presented on the frequency of the composite structure. Results show that with increasing CNTs agglomeration, frequency is decreased.

• Smart Structures and Systems
• /
• 제22권5호
• /
• pp.527-546
• /
• 2018

This article presents an analysis into the nonlinear forced vibration of a micro cylindrical shell reinforced by carbon nanotubes (CNTs) with considering agglomeration effects. The structure is subjected to magnetic field and transverse harmonic mechanical load. Mindlin theory is employed to model the structure and the strain gradient theory (SGT) is also used to capture the size effect. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite cylindrical shell and consider the CNTs agglomeration effect. The motion equations are derived using Hamilton's principle and the differential quadrature method (DQM) is employed to solve them for obtaining nonlinear frequency response of the cylindrical shells. The effect of different parameters including magnetic field, CNTs volume percent and agglomeration effect, boundary conditions, size effect and length to thickness ratio on the nonlinear forced vibrational characteristic of the of the system is studied. Numerical results indicate that by enhancing the CNTs volume percent, the amplitude of system decreases while considering the CNTs agglomeration effect has an inverse effect.

• 한국콘텐츠학회논문지
• /
• 제21권3호
• /
• pp.375-389
• /
• 2021

최근 4차 산업혁명의 시대를 맞아 지역경제의 새로운 성장 동력이 될 것이라고 기대되는 4차 산업에 대한 관심이 높아지고 있다. 이러한 관심을 바탕으로 다양한 정책들이 수립되고 있으나 실제 지역경제에 미치는 영향에 대한 연구는 미흡한 실정이다. 이에 본 연구는 4차 산업의 집적수준의 변화가 지역경제 성장에 미치는 영향을 전국의 시군구를 대상으로 공간통계모형을 사용하여 분석하였다. 분석결과, 4차 산업의 집적이 지역경제의 생산성 측면에는 긍정적인 영향을 주지만 지역의 소득에 대해서는 영향을 준다는 근거를 발견하기 어려웠다. 따라서 4차 산업의 집적이 지역경제에 미치는 영향은 제한적인 것으로 확인되었다. 또한, 4차 산업 유형별로 집적이 지역경제에 미치는 영향이 상이하였으며, 지역경제 영향을 주는 4차 산업혁명 관련 산업은 제조업과 금융 및 보험업의 집적으로 나타났다.

• 대한지리학회지
• /
• 제40권6호
• /
• pp.653-670
• /
• 2005

본 연구는 서울의 경제 환경 변화와 이로 인한 어려움 속에서 전통적인 도시형 제조업이 어떠한 이유와 방식으로 위기에 대응 해가고 있는지를 밝히기 위해, 서울시 제화산업을 사례로 공간적 집적 특성과 혁신환경의 속성을 분석하였다. 분석 결과, 성수동을 중심으로 한 집적지가 성장 중에 있으며, 이 지역을 중심으로 기획 및 디자인, 생산기술, 창업 및 인력수급, 경영 등의 부문에서 국지화된 투입${\cdot}$산출관계와 관련한 정적인 효율성을 넘어 동적 집적경제가 발생할 수 있는 잠재적 요인들이 내재되어 있음을 확인하였다. 이는 최근의 동적 집적경제 접근방식이 전통적인 제조업 집적의 발생과 집적경제의 속성을 설명하는 효과적인 틀이 될 수 있다는 것을 보여주는 것이며, 바로 이러한 분석을 통해 위기에 대응해가는 현 상황에 대한 설명이 가능하다. 그러나 아직 산업을 둘러싼 외적 지원환경과 제도적 플랫폼이 체계적으로 구축되어 있지 못하여, 제화산업집적지가 보다 높은 단계의 산업집적지구로 성장${\cdot}$발전해나가기 위한 전략적 접근이 요구되고 있다.

• World Technopolis Review
• /
• 제3권3호
• /
• pp.122-138
• /
• 2014

The number of environment-related technologies has increased remarkably over the past two decades, as has the public's interest in effective resource use and ways to reduce the effects of global warming. Industries that are based on environment-related technologies are thus growing rapidly. Previous studies revealed that externalities derived from the population concentration in urban areas positively affect agglomerations of high-tech industries. Such externalities have been named the "knowledge spillover effect". The purposes of the present paper are to (1) give a thumbnail sketch of the locations of environment-related industries around the world, using the Organisation for Economic Co-operation and Development environment-related patent statistics, and (2) explicate the effects of the Marshall-Arrow-Romer (MAR) and Jacobs externalities, which result from population concentrations in urban areas, on the agglomeration of environment-related industries in Sweden. The analysis revealed that environment-related industries are located chiefly in urban areas across the globe, and that only the MAR externalities influenced positively on the agglomeration of these industries in Sweden.

• 한국결정성장학회지
• /
• 제9권2호
• /
• pp.224-230
• /
• 1999

콜로이드성 알루미나 분말 입자들의 현탁액에서 입자들의 응집현상을 시뮬레이션 하였다. 현탁액 속의 알루미나 분말 입자들은 입자간 포텐셜 에너지를 가지고 있으며 시간이 경과함에 따라 현탁액으 전체적인 에너지를 감소시키는 방향으로 시스템을 변화시킨다. 현탁액 속의 분말 입자들의 응집 현상을 입자간 포텐셜 곡선의 유형에 따라 관찰하였다. 단거리에서 강한 친화 포텐셜 에너지를 가지는 입자들은 무정형 망목 응집구조를 유도하며 응집체의 크기가 작아지고 단거리에서 강한 척력 포텐셜 에너지와 장거리에서 상대적으로 강한 친화 포텐셜 에너지를 가지는 분말 입자들이 밀집충진 응집구조에 접근하고 응집체의 크기가 상대적으로 커지게 된다. 입자간 에너지 분포에 강한 반발에너지 장벽이 존재하는 경우에 입자들이 응집함에 따라 이러한 에너지는 장벽이 사라지게 되며 이러한 현상은 입자의 응집패턴의 변화를 의미한다.

• Structural Engineering and Mechanics
• /
• 제68권3호
• /
• pp.359-368
• /
• 2018

This paper deals with the dynamic stability of nanocomposite pipes conveying pulsating ferrofluid. The pipe is reinforced by carbon nanotubes (CNTs) where the agglomeration of CNTs are considered based on Mori-Tanaka model. Due to the existence of CNTs and ferrofluid flow, the structure and fluid are subjected to axial magnetic field. Based on Navier-Stokes equation and considering the body forced induced by magnetic field, the external force of fluid to the pipe is derived. For mathematical modeling of the pipe, the first order shear deformation theory (FSDT) is used where the energy method and Hamilton's principle are used for obtaining the motion equations. Using harmonic differential quadrature method (HDQM) and Bolotin's method, the motion equations are solved for calculating the excitation frequency and dynamic instability region (DIR) of the structure. The influences of different parameters such as volume fraction and agglomeration of CNTs, magnetic field, structural damping, viscoelastic medium, fluid velocity and boundary conditions are shown on the DIR of the structure. Results show that with considering agglomeration of CNTs, the DIR shifts to the lower excitation frequencies. In addition, the DIR of the structure will be happened at higher excitation frequencies with increasing the magnetic field.