• Structural Engineering and Mechanics
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• 제68권3호
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• pp.377-384
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• 2018

Bi-stable structure can be stable in both its extended and coiled forms. For the un-stressed thin cylindrical shell, the strain energy expressions are deduced by using a theoretical model in terms of only two parameters. Based on the principle of minimum potential energy, the bi-stable behaviors of the cylindrical shells are investigated. The results indicate that the isotropic cylindrical shell does not have the second stable configuration and laminated cylindrical shells with symmetric or antisymmetric layup of fibers have the second stable state under some confined conditions. In the case of antisymmetric laminated cylindrical shell, the analytical expressions of the stability are derived based on the extremal principle, and the shell can achieve a compact coiled configuration without twist deformation in its second stable state. In the case of symmetric laminated cylindrical shell, the explicit solutions for the stability conditions cannot be deduced. Numerical results show that stable configuration of symmetric shell is difficult to achieve and symmetric shell has twist deformation in its second stable form. In addition, the roll-up radii of the antisymmetric laminated cylindrical shells are calculated using the finite element package ABAQUS. The results show that the value of the roll-up radii is larger from FE simulation than from theoretical analysis. By and large, the predicted roll-up radii of the cylindrical shells using ABAQUS agree well with the theoretical results.

• Structural Engineering and Mechanics
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• 제50권6호
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• pp.797-816
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• 2014

Cooling tower is analyzed as an assembly of layered nonlinear shell elements. Geometric representation of the shell is enabled through layered nonlinear shell elements to define the different layers of reinforcements and concrete by considering the material nonlinearity of each layer for the cooling tower shell. Modal analysis using Ritz vector analysis and nonlinear time history analysis by direct integration method have been carried out to study the effects of the inclination of the supporting columns of the cooling tower shell on its dynamic characteristics. The cooling tower is supported by I-type columns and ${\Lambda}$-type columns supports having the different inclination angles. Relevant comparisons of the dynamic response of the structural system at the base level (at the junction of the column and shell), throat level and at the top of the tower have been made. Dynamic response of the cooling tower is found to be significantly sensitive to the change of the inclination of the supporting columns. It is also found that the stiffness of the structure system increases with increase in inclination angle of the supporting columns, resulting in decrease of the period of the structural system. The participation of the stiffness of the tower in structural response of the cooling tower is fund to be dependent of the change in the inclination angle and even in the types of the supporting columns.

• 폴리머
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• 제34권2호
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• pp.89-96
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• 2010

Methyl methacrylate(MMA), ethyl acrylate(EA), n-butyl acrylate(BA), styrene(St) 단량체를 수용성 개시제인 ammonium persulfate(APS)와 음이온 유화제인 sodium dodecyl benzene sulfonate(SDBS)를 사용하여 organic/organic core-shell 구조의 접착바인더를 중합 후 부직포와 피혁에 함침시키고 플라즈마 표면 처리 후 속도론적인 해석과 기계적인 물성을 평가하였다. Core-shell 바인더 중합시 전환율은 단량체의 조성이 등몰에서 MMA/EA, MMA/BA core-shell 복합입자 모두 90% 이상이 되었다. 등몰에서 부직포/부직포에 core-shell 복합입자를 함침시키고 플라즈마 처리 후의 상태접착 박리강도는 MMA/St, EA/BA, BA/MMA, EA/St, EA/MMA의 순으로 되었고, 또한 부직포/피혁에 core-shell 복합입자를 함침시키고 플라즈마 처리 후의 상태접착 박리강도는 MMA/BA, BA/EA, MMA/EA, St/MMA, EA/St의 순으로 되었다.

• 천문학회보
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• 제36권2호
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• pp.115.1-115.1
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• 2011

We analyzed the line profiles of the planetary nebula (PN) NGC 7009 secured with the Keck I HIES and BOES's spectral data. The 5 positions were taken over the nebular image, 4 points on the bright rim plus 1 point at the central position. The covered spectral wavelength range was $3250{\AA}-8725{\AA}$ in these observations. We decomposed the lines of HI, HeI, HeII, CII, NIII, [ClIII], [NII], [OII], [OIII], [SII], [SIII], [ClIII], and [ArIII] using the IRAF and StarLink/Dipso. After correcting the Earth's movement and the PN's radial velocities, -48.6 & -48.9 km/s, respectively, for the Keck & BOES, we produced the line profiles in a velocity scale. The zero velocity at each line profile clearly indicates which part of the components is approaching or receding, giving a general information of the kinematical structure. Almost all of the low-to-medium excitation lines, such as [NII], [SII], [O III], and [ArIII], secured at the central position and four positions along the major & minor axes, showed 3 components, double peak + a wide wing component, suggesting the fast outflow structures are present. The overall geometry is a prolate shell which also has a fainter outer shell in the halo zone, but there appears to be some peculiar sub-structures inside the main shell. The high excitation He I, HeII, NIII lines which might be formed close to the inner boundary of the shell show unusual features, completely different from the other lines. The HeII and these high excitation lines may be indicative of a relative recent fast outflow from the central star and the permitted lines such as NIII might be affected by the innermost structure. We discuss a possible presence of a jet-like fast outflow structure in an out-flow axis different from the main axis of the spheroid shell.

• Korean Chemical Engineering Research
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• 제52권1호
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• pp.52-57
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• 2014

본 연구에서는 낮은 사이클 안정성을 갖는 MCMB의 단점을 향상시키기 위하여 높은 사이클 안정성과 부피팽창이 없는 장점을 갖는 물질인 $Li_4Ti_5O_{12}$를 코팅하여 core-shell 구조의 $MCMB/Li_4Ti_5O_{12}$를 합성하고 $MCMB/Li_4Ti_5O_{12}$를 음극으로, $LiMn_2O_4$, Active carbon fiber를 양극으로 사용하여 단위 셀을 제조하였다. $LiPF_6$ 염과 EC/DMC/EMC 용매를 전해질로 사용하여 제조한 하이브리드 커패시터 단위 셀로 충방전, 사이클, 순환전압전류, 임피던스 테스트를 진행하여 전기화학적 특성을 평가한 결과, MCMB-$Li_4Ti_5O_{12}/LiMn_2O_4$ 전극을 사용한 하이브리드 커패시터가 MCMB 전극의 하이브리드 커패시터 보다 좋은 충/방전 성능을 보였고, 67 Wh/kg, 781 W/kg의 에너지밀도와 출력밀도를 나타내었다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.428-432
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• 2010

연소기 챔버 노즐확장부 외피구조물의 성형특성에 대한 연구를 수행하였다. 노즐확장부 외피구조물의 제작에 사용되는 냉간압연 판재가 갖는 이방성 특성을 확인하기 위하여 세 가지 방향의 시편을 제작하여 인장시험을 수행하였으며, 그 결과를 이용하여 Lankford 값을 얻어 구조해석에 적용하였다. 실물형 연소기에 사용될 노즐확장부 외피구조물의 제작 및 성형공정을 통하여 외피구조물의 성형특성을 확인하였으며, 성형으로 얻은 변형률들을 구조해석 결과들과 비교하였다. 본 연구에서 얻은 결과들은 확대비가 더 큰 노즐확장부 제작을 위한 치구 및 성형공정의 설계에 활용될 예정이다.

• 한국재료학회지
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• 제32권4호
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• pp.216-222
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• 2022

The capacity of high nickel Li(Ni_xCo_yMn_1-x-y)O₂ (NCM, x ≥ 0.8) cathodes is known to rapidly decline, a serious problem that needs to be solved in a timely manner. It was reported that cathode materials with the {010} plane exposed toward the outside, i.e., a radial structure, can provide facile Li⁺ diffusion paths and stress buffer during repeated cycles. In addition, cathodes with a core-shell composition gradient are of great interest. For example, a stable surface structure can be achieved using relatively low nickel content on the surface. In this study, precursors of the high-nickel NCM were synthesized by coprecipitation in ambient atmosphere. Then, a transition metal solution for coprecipitation was replaced with a low nickel content and the coprecipitation reaction proceeded for the desired time. The electrochemical analysis of the core-shell cathode showed a capacity retention of 94 % after 100 cycles, compared to the initial discharge capacity of 184.74 mA h/g. The rate capability test also confirmed that the core-shell cathode had enhanced kinetics during charging and discharging at 1 A/g.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.293-300
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• 2004

As the structure is taller and its member is larger, the effect of the deformation of Panel zone on the displacement of structure becomes larger. The analysis using the centerline dimensions in the steel moment frame structure can not consider the accurate effect of panel ton And the finite element analysis using infinitesimal solid and shell element is impractical for the total tall building structure. Therefore, this paper proposes the analytical model using linear element in order to be able to evaluate the reasonable deformation of panel zone. the proposed analytical model makes the analysis of the building structure simple and ease because it uses the only linear elements. In addition it can easily incorporate the various parameters affecting the deformation of panel zone. In order to prove the validith of the prosed analytical model, the analysis result using the proposed analytical model is compared with the result using finite element analysis with shell element

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1999년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.275-283
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• 1999

To predict the dynamic behavior of the cylindrical liquid storage tank subjected to seismic ground motion three dimesional analysis with liquid-structure interaction must be performed, In this study a three dimensional dynamic analysis method over the frequency domain using FE-BE coupling technique which combines the efficiency of the boundary elements for liquid with the versatility of the finite shell elements for tank. The liquid region is modeled using boundary elements which can counter the sloshing effect at free surface and the structure region the tank itself is modeled using the degenerated finite shell elements. At the beginning of the procedure the equivalent mass matrix of the liquid is generated by boundary elements procedure. Then this equivalent mass matrix is combined with the mass matrix of the structure to produce the global mass matrix in the equation of the motion of fluid-structure interaction problem In order to demonstrate the accuracy and validity of the developed method the numerical results re compared with the previous studies. Finally the effects of the fluid-structure interaction on the natural frequency and dynamic response of the system are analyzed.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.234-241
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• 1999

In this study, an improved 8-node flat shell element is presented for the analysis of shell structure, by combining 8-node membrane element with drilling degree-of-freedom and 8-node plate bending element based on the recently presented technique. Firstly, 8-node membrane element designated as CLM8 is presented in this paper. The element has drilling degree-of.freedom in addition to transitional degree-of-freedom. Therefore the element possesses 3 degrees-of-freedom per each node which as well as the improvement of the element behavior, permits an easy connection to other element with rotational degree-of -freedom. Secondly. 8-node flat shell element was composed by adding 8-node Mindlin plate bending element to the membrane element. The behavior of the introduced plate bending element is further improved by combined use of nonconforming displacement modes, selectively reduced integration scheme and assumed shear strain fields. The element passes in the patch test, doesn't show spurious mechanism and doesn't produce shear locking phenomena. Finally, Numerical examples are presented to show the performance of flat shell element developed in the present study.