• Steel and Composite Structures
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• 제31권3호
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• pp.261-276
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• 2019

The study investigates the free vibration of a nano-scale sandwich beam by an extended high order approach, which has not been reported in the existing literature. First-order shear deformation theory for steel skins and so-called high-order sandwich panel theory for the core are applied. Next, the modified couple stress theory is used for both skins and cores. The Hamilton principle is utilized for deriving equations and corresponding boundary conditions. First, in the study the three-mode shapes natural frequencies for various material parameters are investigated. Also, obtained results are evaluated for two types of stiff and soft cores and isotropic, homogenous steel skins. In the research since the governing equations and also the boundary conditions are nonhomogeneous, therefore some closed-form solutions are not applicable. So, to obtain natural frequencies, the boundary conditions are converted to initial conditions called the shooting method as the numerical one. This method is one of the most robust approaches to solve complex equations and boundary conditions. Moreover, three types of simply supported on both sides of the beam (S-S), simply on one side and clamp supported on the other one (S-C) and clamped supported on both sides (C-C) are scrutinized. The parametric study is followed to evaluate the effect of nano-size scale, geometrical configurations for skins, core and material property change for cores as well. Results show that natural frequencies increase by an increase in skins thickness and core Young modulus and a decrease in beam length, core thickness as well. Furthermore, differences between obtained frequencies for soft and stiff cores increase in higher mode shapes; while, the more differences are evaluated for the stiff one.

• Advances in nano research
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• 제10권5호
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• pp.449-460
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• 2021

Flexoelectricity is an interesting materials' property that is more touchable in small scales. This property beside the sandwich structures placed in the center of scientists' attention due to their extraordinary effects on the mechanical properties. Furthermore, in the passage of decades, more elaborated sandwich structures took into consideration results from using honeycomb core. This kind of structure, inspiring from honeycomb core, provides more stiffness to weight ratio, which plays a crucial role in different industries. In this paper, based on the Love-Kirchhoff's hypothesis, Hamilton's principle, modified couple stress theory and Fourier series analytical method, equations of motion for a sandwich plate containing a honeycomb core integrated by two face-sheets have derived and solved analytically. The equations of both face sheets have derived by flexoelectricity consideration. Moreover, it should be noticed that the whole structure rests on the visco-Pasternak foundation. Conducting current research provided an acceptable and throughout study based on flexoelectricity to address the effect of materials' characteristics, length-scale parameter, aspect, and thickness ratios and boundary conditions on the natural frequency of honeycomb sandwich plates. Also, based on the presented figures and tables, there is a close agreement between previous studies and recent work. Due to the high ratio of strength to weight, current model analyzing is capable of taking into account for different vehicles' manufacturing in a high range of industries.

• Steel and Composite Structures
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• 제43권1호
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• pp.79-90
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• 2022

In this study, the dynamic behavior of functionally graded layered deep beams with viscoelastic core is investigated including the porosity effect. The material properties of functionally graded layers are assumed to vary continuously through thickness direction according to the power-law function. To investigate porosity effect in functionally graded layers, three different distribution models are considered. The viscoelastically cored deep beam is exposed to harmonic sinusoidal load. The composite beam is modeled based on plane stress assumption. The dynamic equations of motion of the composite beam are derived based on the Hamilton principle. Within the framework of the finite element method (FEM), 2D twelve -node plane element is exploited to discretize the space domain. The discretized finite element model is solved using the Newmark average acceleration technique. The validity of the developed procedure is demonstrated by comparing the obtained results and good agreement is detected. Parametric studies are conducted to demonstrate the applicability of the developed methodology to study and analyze the dynamic response of viscoelastically cored porous functionally graded deep beams. Effects of viscoelastic parameter, porosity parameter, graduation index on the dynamic behavior of porous functionally graded deep beams with viscoelastic core are investigated and discussed. Material damping and porosity have a significant effect on the forced vibration response under harmonic excitation force. Increasing the material viscosity parameters results in decreasing the vibrational amplitudes and increasing the vibration time period due to increasing damping effect. Obtained results are supportive for the design and manufacturing of such type of composite beam structures.

• Steel and Composite Structures
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• 제47권6호
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• pp.743-757
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• 2023

In this paper, the dynamic response of a simply-supported composite sandwich plate with a viscoelastic core based on the Golla-Hughes-McTavish (GHM) viscoelastic model is investigated analytically. The formulation is developed using the three-layered sandwich panel theory. Hamilton's principle has been employed to derive the equations of motion. Since classical models, like kelvin-voigt and Maxwell models, cannot express a comprehensive description of the dynamic behavior of viscoelastic material, the GHM method is used to model the viscoelastic core of the plate in this research. The main advantage of the GHM model in comparison with classical models is the consideration of the frequency-dependent characteristic of viscoelastic material. Identification of the material parameters of GHM mini-oscillator terms is an essential procedure in applying the GHM model. In this study, the focus of viscoelastic modeling is on the development of GHM parameters identification. For this purpose, a new method is proposed to find these constants which express frequency-dependent behavior characterization of viscoelastic material. Natural frequencies and loss factors of the sandwich panel based on ESL and three-layered theories in different geometrics are described at 30℃ and 90℃; also, the comparisons show that obtained natural frequencies are grossly overestimated by ESL theory. The argumentations of differences in natural frequencies are also illustrated in detail. The obtained results show that the GHM model presents a more accurate description of the plate's dynamic response by considering the frequency dependency behavior of the viscoelastic core.

• 지질공학
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• 제24권3호
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• pp.423-429
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• 2014

본 연구에서는 국내 비전통에너지자원인 셰일가스, 석탄층메탄가스(CBM) 및 가스하이드레이트 개발사업의 정확한 매장량을 위해 온도와 압력을 실시간으로 기록하는 DLS (Data Logging System)가 내장된 저류층 PCS (Pressure Core Sampler)를 개발하여 국산화시키고, 지하심부의 시료가 채취된 순간부터 시료의 압력을 유지함으로써 시료 내 가스의 손실 없이 시추코어를 회수하는데 있다. 저류층 PCS는 일반적인 코어 샘플러와는 달리 입구 부분에 볼밸브와 같은 개폐 장치가 있어 일정 길이의 코어 샘플이 채취되면 입구를 밀폐하여 원위치 상태의 압력이 그대로 유지되게 하는 기능을 갖고 있다. 이것은 특히 셰일가스나 석탄층메탄가스 및 가스하이드레이트와 같은 기체를 포함한 시료의 정확한 분석을 위해 아주 중요한 역할을 하게 된다. 현재 PCS 장비 및 이를 활용한 기술은 미국과 유럽 등에서 독점하고 있는 상황이다. 이에 따라 기존 PCS의 동작원리 및 메커니즘 분석과 상세설계를 수행하여 저류층PCS를 개발중이며, 성능은 PCS 최대 사용압력 100 bar, PCS 최대 사용온도 $-20{\sim}40^{\circ}C$, PCS 압력 손실율 10%를 목표로 하고 있다.

• 한국실내디자인학회논문집
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• 제18권2호
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• pp.33-40
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• 2009

Reflecting the idea of benevolent royal government of King Jeongjo(鼎俎), the Buyongji(芙蓉池) and Juhamru(宙合樓) of Changdeokgung(昌德宮) are the traditional Korean architecture to represent the Joseon(朝鮮) period. The purposes of this study were to investigate how the Likiron(理氣論), one of the foremost theories of Joseon Confucianism, was applied to the principle of space composition by analyzing Buyongji and Juhamru with Jung's analytical psychology and to provide basic data to utilize the results in modem space planning. The research findings indicate that Buyongji is the space of Ki(氣) to reflect the reality, corresponds to conscious, and represents the Joseon land and people including Chiljeong(七情) And Juhamru is the space of Li(理) with the ideal of benevolent royal government inherited in it and represents unconscious. It also has each building placed which contained the nature of Sadan(四端) along with Gyujanggak and Jewolgwangpunggwak(齊月光風觀) to represent "Self Archetype" that's the core of human mind. Each representing Ki and Li, Buyongji and Juhamru must have worked as a major composition principle of Likilwonronjeokilwonron(理氣二元論的一元論) that could simultaneously satisfy the practice philosophy of reality and ideal among Likiron.

• Ocean and Polar Research
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• 제28권2호
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• pp.175-186
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• 2006

There are disputes for oil and gas development between China and Japan in the East China Sea. These involve the area where China is already carrying out activities of oil and gas development and where Japan is proclaiming its EEZ. China insists that the Chinese activities on oil and gas development area are being carried out within the Chinese jurisdictional waters even if the median line principle of Japanese proclamation is applied in delimitation. Indeed, the permit for Japanese development is causing disputes between China and Japan because its permit allows development in the waters adjacent to Chinese development area. h the event, the core of this dispute around the oil and gas field in the East China Sea relates to issues of maritime boundary delimitation and issues of resources acquisition with both states. Chinese policy on oil and gas development is to first consider development issues in accordance with a median line principle where waters toward to China from the median line should be developed by China and the area toward Japan from the median line within the Chinese continental shelf should be jointly developed. However, the Japanese position is that the East China Sea should be jointly developed, and Japan hopes to eventually convince China to accept its median line delimitation. With on-going development of such issues, Korea should establish a strategy of negotiation based on analyses of resource distributional conditions and other strategic factors in the Korean delimitation area. In particular, Korea should prepare and make the best use of joint development zone established in an agreement between the ROK and Japan concerning the development of the southern part of continental shelf adjacent to both states.

• 의정연구
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• 제27권1호
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• pp.157-185
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• 2021

지방세 납세지는 납세행위가 이루어지는 장소적 개념만이 아니라 자치단체의 과세권이 결정되는 현실적인 의미를 가진다. 납세지 결정에는 납세의 편의성이나 징세의 효율성을 넘어 편익지역의 원칙이라는 지방세의 핵심 과세기준이 중요하게 고려되어야 한다. 대부분 지방세의 납세지 설정에 있어 편익지역의 원칙이 비교적 잘 반영되고 있는 것으로 평가된다. 그러나 소득세와 과세표준을 공유하는 지방소득세의 경우 납세지 설정에 개편의 필요성이 있는데, 사업소득과 부동산 등의 양도소득에 대한 과세지를 주소지에서 사업장 소재지와 부동산 등의 소재지로 변경하는 방안을 검토해야 한다. 근로나 사업영위 등 제반 소득활동을 통해 소득이 창출되는 데 있어 지방자치단체의 공공서비스의 편익이 기여하고 있다는 점에서 그 소득활동이 이루어지는 편익지역에서 과세가 이루어지도록 할 필요가 있다. 이러한 개편으로 자치단체 간의 세수불균형도 일정부분 완화될 수 있는 것으로 평가되며, 납세와 징세의 측면에서도 일정한 긍정적인 효과가 예상된다.

• Smart Structures and Systems
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• 제25권2호
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• pp.197-218
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• 2020

In this work, thermomechanical flexural analysis of functionally graded material sandwich plates with P-FGM face sheets and E-FGM and symmetric S-FGM core is performed by employing a nth-order shear deformation theory. A novel type of S-FGM sandwich plates, namely, both P-FGM face sheets and a symmetric S-FGM hard core are considered. By employing only four unknown variables, the governing equations are obtained based on the principle of virtual work and then Navier method is used to solve these equations. Analytical solutions are deduced to compute the stresses and deflections of simply supported S-FGM sandwich plates. The effects of volume fraction variation, geometrical parameters and thermal load on thermomechanical flexural behavior of the symmetric FGM sandwich plates are investigated.

• 한국해양공학회지
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• 제33권6호
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• pp.535-546
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• 2019

The paper presents a closed-form analytical solution for the ultimate strength of sandwich panels with metal faces and an elastic isotropic core during combined in-plane compression and lateral pressure under clamped boundary condition. By using the principle of minimum potential energy, the stress distribution in the faces during uni-axial edge compression and constant lateral pressure was obtained. Then, the ultimate edge compression was derived on the basis that collapse occurs when yield has spread from the mid-length of the sides of the face plates to the center of the convex face plates. The results were validated by nonlinear finite element analysis. Because the solution is analytical and closed-form, it is rapid and efficient and is well-suited for use in practical structural design methods, including repetitive use in structural optimization. The solution applies for any elastic isotropic core material, but the application that stimulated this study was an elastomer-cored steel sandwich panel that had excellent energy absorbing and protective properties against fire, collisions, ballistic projectiles, and explosions.