• Steel and Composite Structures
• /
• 제44권1호
• /
• pp.65-79
• /
• 2022

The main goal of this paper is to study the vibration of damaged core laminated annular plates with FG face sheets based on a three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. In this study the effect of microcracks on the vibrational characteristic of the sandwich plate is considered. In particular, the structures are made by an isotropic core that undergoes a progressive uniform damage, which is modeled as a decay of the mechanical properties expressed in terms of engineering constants. These defects are uniformly distributed and affect the central layer of the plates independently from the direction, this phenomenon is known as "isotropic damage" and it is fully described by a scalar parameter. Three complicated equations of motion for the sectorial plates under consideration are semi-analytically solved by using 2-D differential quadrature method. Using the 2-D differential quadrature method in the r- and z-directions, allows one to deal with sandwich annular plate with arbitrary thickness distribution of material properties and also to implement the effects of different boundary conditions of the structure efficiently and in an exact manner. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. The sandwich annular plate is assumed to have any arbitrary boundary conditions at the circular edges including simply supported, clamped and, free. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution, and boundary conditions.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.297.2-297.2
• /
• 2016

Photoacoustic generation of ultrasound is an effective approach for development of high-frequency and high-amplitude ultrasound transmitters. This requires an efficient energy converter from optical input to acoustic output. For such photoacoustic conversion, various light-absorbing materials have been used such as metallic coating, dye-doped polymer composite, and nanostructure composite. These transmitters absorb laser pulses with 5-10 ns widths for generation of tens-of-MHz frequency ultrasound. The short optical pulse leads to rapid heating of the irradiated region and therefore fast thermal expansion before significant heat diffusion occurs to the surrounding. In this purpose, nanocomposite thin films containing gold nanoparticles, carbon nanotubes (CNTs), or carbon nanofibers have been recently proposed for high optical absorption, efficient thermoacosutic transfer, and mechanical robustness. These properties are necessary to produce a high-amplitude ultrasonic output under a low-energy optical input. Here, we investigate carbon nanotube (CNT)-polydimethylsiloxane (PDMS) composite transmitters and their nanostructure-originated characteristics enabling extraordinary energy conversion. We explain a thermoelastic energy conversion mechanism within the nanocomposite and examine nanostructures by using a scanning electron microscopy. Then, we measure laser-induced damage threshold of the transmitters against pulsed laser ablation. Particularly, laser-induced damage threshold has been largely overlooked so far in the development of photoacoustic transmitters. Higher damage threshold means that transmitters can withstand optical irradiation with higher laser energy and produce higher pressure output proportional to such optical input. We discuss an optimal design of CNT-PDMS composite transmitter for high-amplitude pressure generation (e.g. focused ultrasound transmitter) useful for therapeutic applications. It is fabricated using a focal structure (spherically concave substrate) that is coated with a CNT-PDMS composite layer. We also introduce some application examples of the high-amplitude focused transmitter based on the CNT-PDMS composite film.

• 한국강구조학회 논문집
• /
• 제17권2호통권75호
• /
• pp.173-181
• /
• 2005

본 연구는 유한요소법과 고도화된 마이크로 유전알고리즘을 조합하여 자유 진동하는 박판 구조물에 대한 손상 규명을 다룬다. 조합된 방법에 의해 역 문제를 해결하기 위하여, 본 연구는 측정 데이터로서 구조물의 모드 형상 대신 몇 개의 고유진동수를 사용한다. 본 연구에서 제안한 방법은 손상된 요소를 탐지할 수 있을 뿐만 아니라 손상의 개수, 위치 그리고 정도를 추정할 수 있다. 제안된 방법의 타당성을 검증하기 위하여 알고리즘은 임의의 손상을 갖는 강으로 된 지유진동 박판 구조물을 대상으로 적용하였다. 기존의 단순 유전알고리즘에 비하여 본 연구에서 제안한 알고리즘은 수치적 효율성에서 큰 장점을 갖는다. 수치해석 예제들은 고유모드 대신 단지 몇 개의 고유진동수 값만으로도 마이크로 유전알고리즘은 박판의 손상을 정확히 규명할 수 있음을 보여준다.

• 통상정보연구
• /
• 제12권3호
• /
• pp.79-98
• /
• 2010

The National Conference of Commissioners on Uniform State Laws promulgated the Uniform Computer Information Transactions Act (UCITA) in 1999. In 2000 and 2002, this Act was also Amended. UCITA provides a comprehensive set of rules for licensing computer information, whether computer software or other clearly identified forms of computer information. Computerized databases and computerized music are other examples of computer information that would be subject to UCITA. It would also govern access contracts to sites containing computer information, whether on or off the Internet. UCITA would not govern contracts, even though they may be licensing contracts, for the traditional distribution of movies, books, periodicals, newspapers, or the like. Part 8 of UCITA provides a remedy structure somewhat modeled on that of Article 2 but adapted in significant respects to the different context of a computer information transaction. For example, 808 of UCITA recognizes the focus in a license context for a licensor's remedy should properly be on recovery for benefit conferred or for lost profit, rather than on damage measurement by a substitute transaction, where the license is non-exclusive so additional transactions are permitted and there is very little cost in reproduction of the information and its redistribution. Section 816 of UCITA also contains very important limitations on the generally recognized common law right of self-help as applicable in the electronic context.

• Composites Research
• /
• 제29권5호
• /
• pp.299-305
• /
• 2016

본 연구는 이변량 Gaussian 분포함수를 적용하여 CFRP 적층판의 섬유물성 변화를 추정하는 방법을 제안하였다. 섬유의 손상 분포를 규명하기 위하여 수정된 이변량 Gaussian 분포함수를 적용하여 5개의 미지 변수가 고려되었다. 조합된 컴퓨터 기법을 적용하여 역문제를 해결하기 위하여 본 연구에서는 몇 개의 고유진동수와 모드 정보를 입력데이터로 활용하였다. 수치해석 예제는 제안된 기법이 적층배열 변화에 따른 CFRP 판의 섬유 손상 분포 및 위치를 규명할 수 있는 적합하고 실용적은 방법임을 보여준다.

• Smart Structures and Systems
• /
• 제26권3호
• /
• pp.345-360
• /
• 2020

Modern swarm intelligence heuristic search methods are widely applied in the field of structural health monitoring due to their advantages of excellent global search capacity, loose requirement of initial guess and ease of computational implementation etc. To this end, a hybrid strategy is proposed based on butterfly optimization algorithm (BOA) and differential evolution (DE) with purpose of effective combination of their merits. In the proposed identification strategy, two improvements including mutation and crossover operations of DE, and dynamic adaptive operators are introduced into original BOA to reduce the risk to be trapped in local optimum and increase global search capability. The performance of the proposed algorithm, hybrid butterfly optimization and differential evolution algorithm (HBODEA) is evaluated by two numerical examples of a simply supported beam and a 37-bar truss structure, as well as an experimental test of 8-story shear-type steel frame structure in the laboratory. Compared with BOA and DE, the numerical and experimental results show that the proposed HBODEA is more robust to detect the reduction of stiffness with limited sensors and contaminated measurements. In addition, the effect of search space, two dynamic operators, population size on identification accuracy and efficiency of the proposed identification strategy are further investigated.

• Advances in concrete construction
• /
• 제15권3호
• /
• pp.203-213
• /
• 2023

New techniques, technologies, and materials should be used to design and build sports stadiums. Since this century, much progress has been made in covering the roofs of sports stadiums, and the possibility of accurate computer calculation has been provided for stadiums, so by choosing a new structure, we can double the beauty and resistance of these stadiums. A stadium has an excellent and valuable design when its structure, shell, building, materials, and joinery follow a high architectural idea at all levels and scales. This article examines the mechanical performance of polymer cement strength in the construction of football stadiums, along with their structural knowledge in the form of the best examples in the world. Portland cement is one of the most used materials for constructing football stadiums. However, its production requires spending a lot of money, wasting energy, and damaging the environment. Considering the disadvantages in the production and consumption of concrete in different environments, it is necessary to find alternative materials. It should be used with cheaper, simpler technology, abundant primary resources, energy saving, less environmental damage, and better chemical and physical properties in concrete. High-strength concrete technology is considered a new development in the construction industry of concrete structures. In hardened concrete, strength and durability are two main factors, and as the compressive strength of concrete increases, concrete becomes more brittle. As a result, its tensile strength does not increase in proportion to the increase in compressive strength and has less strain tolerance. For this reason, the need to use is evident from the fibers in high-strength concrete. Fibers are used in concrete to increase tensile strength, prevent crack propagation, and significantly increase softness. The increase with the change of these resistances depends on the strength of concrete without fibers, the shape of fibers, and the percentage of fibers. This cement is obtained from the wastes of chemical and petrochemical industries and the wastes from coal combustion, which have the properties mentioned as substitutes for Portland cement.

• 한국건설관리학회:학술대회논문집
• /
• 한국건설관리학회 2007년도 정기학술발표대회 논문집
• /
• pp.643-646
• /
• 2007

도심지 지가가 높아짐에 따라 건축물의 공간 활용도에 대한 기대치가 높아지게 되었고, 건축물은 더 크고, 더 깊고, 더 높게 지어지는 방향으로 나아가고 있다. 이에 따라, 공사의 첫 단계이자 전체 건물의 기초가 되는 지하 공사는 그 중요성이 날로 더해가고 있다. 최소한의 비용으로 최단기간에 터파기 공사를 완료해야 하는 도심지 공사의 특성상 공사 관계자들은 지하 공사를 계획, 설계, 시공, 설계하는 과정에서 심혈을 기울이고 있다. 그럼에도 불구하고 지하 공사 전번에 걸쳐 있는 불확실성과 위험 요소 때문에 공사 실패 사례가 발생하고 있다. 더욱이 이러한 사고가 어느 정도의 경제적 피해를 끼쳤는지에 대한 보고나 연구없이 사고 사례만 알려지기 때문에 지하 공사의 위험성에 대한 경각심이 부족한 것이 우리나라 건축의 현실이다. 이런 사고를 타산지석으로 삼아 터파기 공사 공법을 선정하고 지하 공사를 이행하는데 있어서 하나의 지침이 되기를 바라면서 지하 공사 실패 사례가 과연 어느 정도의 경제적 피해를 발생시키는지를 개산견적 기법을 도입하여 추정해 보았다.

• Steel and Composite Structures
• /
• 제48권1호
• /
• pp.1-17
• /
• 2023

The main goal of this paper is to study vibration of damaged core laminated sectorial plates with Functionally graded (FG) face sheets based on three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. Three complicated equations of motion for the sectorial plates under consideration are semi-analytically solved by using 2-D differential quadrature method. Using the 2-D differential quadrature method in the r- and z-directions, allows one to deal with sandwich annular sector plate with arbitrary thickness distribution of material properties and also to implement the effects of different boundary conditions of the structure efficiently and in an exact manner. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. The sandwich annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution and boundary conditions.

• 대한조선학회논문집
• /
• 제36권4호
• /
• pp.137-146
• /
• 1999

선체구조는 많은 수의 구조부재로 이루어져 있으며, 구조물의 안정성을 확보하기 위해 모든 부위의 검사를 위해서는 경제적, 사회적인 많은 비용이 필요하므로, 검사시기 및 검사방법의 최적화는 선체구조의 안정성확보 및 경제적 관점에서 매우 중요한 부분이 되고 있다. 선체구조 손상중 많은 부분이 균열이며 이러한 미세한 균열이 성장하여 대규모 파괴로 진전되기 전에 검사를 통하여 균열을 검출하고 수리하는 과정을 Markov 연쇄모델에 의해 이상화 시켰으며, 검사 계획안의 최적화는 유전적 알고리즘을 통하여 구현하였다. 특히 선박은 부식환경하에서 운항하므로 부식에 의한 선체구조부재의 치수가 감소하기 때문에 응력이 변하고 균열진전의 확률적인 특성 또한 변한다. 정상 Markov 연쇄모델로서는 이러한 부식에 의한 영향을 고려할수 없기 때문에 비정상 Markov 연쇄모델에 의해 부식의 영향을 고려하였다. 여러개의 부재군에 대한 검사 계획안의 최적화에 대하여 수치계산을 실시하여 그 특성을 비교하였고, 부식영향하의 부재군에 대하여 검사기간중에 발생되는 고정비용의 정도에 따른 경제성 분석 및 목표 파괴확률의 정도에 따른 검사계획의 차이를 살펴보았다. 수치계산 예를 통하여 전체비용을 줄이기 위해서는 피로수명이 짧은 부재군에 대한 피로수명을 향상시키는 방안이 가장 효율적임을 알 수 있다.