Lead-free perovskite ceramics, which have excellent energy storage capabilities, are attracting attention owing to their high power density and rapid charge-discharge speed. Given that the energy-storage properties of perovskite ceramic capacitors are significantly improved by doping with various elements, modifying their chemical compositions is a fundamental strategy. This study investigated the effect of Zn doping on the microstructure and energy storage performance of potassium sodium niobate (KNN)-based ceramics. Two types of powders and their corresponding ceramics with compositions of (1-x)(K,Na)NbO3-xBi(Ni2/3Ta1/3)O3 (KNN-BNT) and (1-x)(K,Na)NbO3-xBi(Ni1/3Zn1/3Ta1/3) O3 (KNN-BNZT) were prepared via solid-state reactions. The results indicate that Zn doping retards grain growth, resulting in smaller grain sizes in Zn-doped KNN-BNZT than in KNN-BNT ceramics. Moreover, the Zn-doped KNNBNZT ceramics exhibited superior energy storage density and efficiency across all x values. Notably, 0.9KNN-0.1BNZT ceramics demonstrate an energy storage density and efficiency of 0.24 J/cm3 and 96%, respectively. These ceramics also exhibited excellent temperature and frequency stability. This study provides valuable insights into the design of KNNbased ceramic capacitors with enhanced energy storage capabilities through doping strategies.

Recently, due to high theoretical capacitance and excellent ion diffusion rate caused by the 2D layered crystal structure, transition metal hydroxides (TMHs) have generated considerable attention as active materials in supercapacitors (or electrochemical capacitors). However, TMHs should be designed using morphological or structural modification if they are to be used as active materials in supercapacitors, because they have insulation properties that induce low charge transfer rate. This study aims to modify the morphological structure for high cycling stability and fast charge storage kinetics of TMHs through the use of nickel cobalt hydroxide [NiCo(OH)2] decorated on nickel foam. Among the samples used, needle-like NiCo(OH)2 decorated on nickel foam offers a high specific capacitance (1110.9 F/g at current density of 0.5 A/g) with good rate capability (1110.9 - 746.7 F/g at current densities of 0.5 - 10.0 A/g). Moreover, at a high current density (10.0 A/g), a remarkable capacitance (713.8 F/g) and capacitance retention of 95.6% after 5000 cycles are noted. These results are attributed to high charge storage sites of needle-like NiCo(OH)2 and uniformly grown NiCo(OH)2 on nickel foam surface.

When an unexpected excessive seismic load is applied to the base isolation of arch structure, the seismic displacement of the base isolation may be very large beyond the limit displacement of base isolation. These excessive displacement of the base isolation causes a large displacement in the upper structure and large displacement of upper structure causes structural damage. Therefore, in order to limit the seismic displacement response of the base isolation, it is necessary to install an additional device such as an anti-uplift device to the base isolation. In this study, the installation direction of the base isolation and the control performance of the base isolation installed anti-uplift device were investigated. The installation direction of the base isolation of the arch structure is determined by considering the horizontal and vertical reaction forces of the arch structure. In addition, the separation distance of the anti-uplift device is determined in consideration of the design displacement of the base isolation and the displacement of the arch structure.

Recently, deep learning that is the most popular and effective class of machine learning algorithms is widely applied to various industrial areas. A number of research on various topics about structural engineering was performed by using artificial neural networks, such as structural design optimization, vibration control and system identification etc. When nonlinear semi-active structural control devices are applied to building structure, a lot of computational effort is required to predict dynamic structural responses of finite element method (FEM) model for development of control algorithm. To solve this problem, an artificial neural network model was developed in this study. Among various deep learning algorithms, a recurrent neural network (RNN) was used to make the time history response prediction model. An RNN can retain state from one iteration to the next by using its own output as input for the next step. An eleven-story building structure with semi-active tuned mass damper (TMD) was used as an example structure. The semi-active TMD was composed of magnetorheological damper. Five historical earthquakes and five artificial ground motions were used as ground excitations for training of an RNN model. Another artificial ground motion that was not used for training was used for verification of the developed RNN model. Parametric studies on various hyper-parameters including number of hidden layers, sequence length, number of LSTM cells, etc. After appropriate training iteration of the RNN model with proper hyper-parameters, the RNN model for prediction of seismic responses of the building structure with semi-active TMD was developed. The developed RNN model can effectively provide very accurate seismic responses compared to the FEM model.

바람하중을 받는 고층건물의 진동을 저감하기 위한 다양한 진동제어장치가 적용되어왔다. 제어의 주된 목적은 구조물의 응답을 저감하는 것이지만 효율적인 제어력의 산정 또한 중요한 설계요구사항중의 하나이다. 능동형제진장치를 중심으로 제어력 산정은 크게 시스템의 H2, H∞-norm을 분리하여 독립적으로 결정되어 왔다. 보다 효율적인 제어력 산정을 위해서 두 가지 norm을 혼합한 제어알고리듬이 개발되었고 이를 LMI 표준형으로 변환하여 보다 용이하게 최적 해를 제공하게 되었다. 본 연구에서는 제어 후 구조물의 요구 등가감쇠비를 H∞-norm을 이용하여 구속하고 제어력만을 별도로 H2-norm을 이용한 제어알고리듬을 개발하여 능동형뿐만 아니라 수동형제진장치에도 적용하는 방안을 제시하였다. 본 연구에서 제안된 혼합제어 기법을 능동질량감쇠기와 카고메 트러스 댐퍼가 설치된 구조물에 적용하여 수치적으로 검증하였으며, 수치해석 결과로부터 능동형뿐만 아니라 수동형제진장치설계를 LMI표준형으로 전환하는 기법을 적용하면 제어이득뿐만 아니라 감쇠용량도 효율적으로 산정 가능함을 알 수 있었다.

In this study, the retractable-roof spatial structure was chosen as the analytical model and a tuned mass damper (TMD) was installed in the analytical model in order to control the seismic response. The analysis model is mainly consisted of runway trusses (RT) and transverse trusses (TT), and the displacement response was analyzed by installing TMD on those trusses. The mass of the single TMD which is installed in the analytical model was set to 1% of the total structure mass and the total TMD mass ratio was set to be 8% or 6%. In addition, the mass of a single TMD was varied depending on the number of installations. As a result of analyzing the optimal number of installations of TMD, the displacement response was reduced in all cases compared to the case without TMD. Above all, the case with 8 TMDs was the most effective in reducing he displacement response. However, in this case, as the load on the upper structure of the retractable-roof spatial structure increases, the total mass ratio of TMD was maintained and the number of TMDs was increased to reduce the mass ratio of one TMD.

In this study, the seismic response is investigated by using a relatively low-rise building under torsion-prone conditions and three seismic loads with change of the location of the seismic isolation system. LRB (Lead Rubber Bearing) was used for the seismic isolator applied to the analytical model. Fixed model without seismic isolation system was set as a basic model and LB models using seismic isolation system were compared. The maximum story drift ratio and the maximum torsional angle were evaluated by using the position of the seismic layer as a variable. It was confirmed that the isolation device is effective for torsional control of planar irregular structures. Also, it was shown that the applicability of the midstory seismic isolation system. Numerical analyses results presented that an isolator installed in the lower layer provided good control performance for the maximum story drift ratio and the maximum torsional angle simultaneously.

A smart connective control system was invented recently for coupling control of adjacent buildings. Previous studies on this topic focused on development of control algorithm for the smart connective control system and design method of control device. Usually, a smart control devices are applied to building structures after structural design. However, because structural characteristics of building structure with control devices changes, a iterative design is required for optimal design. To defeat this problem, an integrated optimal design method for a smart connective control system and connected buildings was proposed. For this purpose, an artificial seismic load was generated for control performance evaluation of the smart coupling control system. 20-story and 12-story adjacent buildings were used as example structures and an MR (magnetorheological) damper was used as a smart control device to connect adjacent two buildings. NSGA-II was used for multi-objective integrated optimization of structure-smart control device. Numerical simulation results show the integrated optimal design method proposed in this study can provide various optimal designs for smart connective control system and connected buildings presenting good control performance.

In the precedent study, the retractable-roof spatial structure was selected as the analytical model and a tuned mass damper (TMD) was installed to control the dynamic response for the earthquake loads. Also, it is analyzed that the installation location of TMD in the analytical model and the optimal number of installations. A single TMD mass installed in the analytical model was set up 1% of the mass of the whole structure, and the optimum installation location was derived according to the number of change. As a result, it was verified that most effective to install eight TMDs regardless of opening or closing. Thus, in this study, eight TMDs were installed in the retractable-roof spatial structure and the optimum mass ratio was inquired while reducing a single TMD. In addition, the optimum mass distribution ratio was identified by redistributing the TMD masses differently depending on the installation position, using the mass ratio of vibration control being the most effective for seismic load. From the analysis results, as it is possible to confirm the optimum mass distribution ratio according to the optimum mass ratio and installation location of the TMD in the the retractable-roof spatial structure, it can be used as a reference in the TMD design for large space structure.

Dual porous structures are observed for the first time on a metallic Cu surface underneath anodic Cu oxide by the application of an anodizing voltage to Cu in oxalic acid. The as-prepared porous Cu surface contains macropores of less than 1 μm diameter and mesopores of about tens of nanometers diameter with circular shapes. The size and density (number of pores/area) of the macropores are dependent on the applied voltage. It is likely that the localized dissolution (corrosion) of Cu in oxalic acid under the anodizing voltages is responsible for the formation of the mesopores, and the combination of a number of the mesopores might create the macropores, especially under a relatively high anodizing voltages or a prolonged anodizing time. The variations of pore structure (especailly macropores) with applied voltage and time are reasonably explained on the basis of the proposed mechanism of pore formation.

이 논문에서는 다중 재난을 고려한 복합 구조제어 시스템의 최적 설계방법을 제시한다. 한 가지 유형의 위험에 대해 하나의 시스템이 설계되는 전형적인 구조제어 시스템과는 달리, 구조물의 지진 및 바람에 의한 진동응답을 저감하기 위해 능동 및 수동제어 시스템에 대한 동시 최적 설계방법을 제안하였다. 수치 예로서, 30층 빌딩 구조물에 설치된 30개의 점성 댐퍼와 복합형 질량 감쇠기에 대한 최적 설계문제를 보였다. 최적화 문제를 풀기 위해 자체적응 화음탐색(harmony search, HS)알 고리즘을 채택하였다. 화음탐색 알고리즘은 사람이 연주하는 악기의 튜닝 과정을 모방한 전역 최적화를 위한 메타 휴리스틱 진화 연산방법의 하나이다. 또한 전역 탐색 및 빠른 수렴을 위해 자가적응적이고 동적인 매개변수 조정 알고리즘을 도입하였다. 최적화 설계 결과, 능동 및 수동 시스템이 독립적으로 최적화된 표준적인 복합제어 시스템에 비해 제안한 동시 최적제어 시스템의 성능과 효율성이 우수함을 보였다.

본 연구에서는 상전이법을 이용하여 P(VDF-co-HFP) 분리막의 구조를 조절하였다. Macrovoid 없는 구조를 얻기 위하여 다양한 조건에서 비용매유도상전이(NIPS) 공법으로 분리막을 제막하였으나 고분자의 낮은 결정화 속도로 인해 macrovoid가 생성된다는 것을 관측하였다. 이를 극복하기 위해 증발유도상전이법(EIPS)과 증기유도상전이법(VIPS)을 도입하였으며 NIPS공법과 함께 제막되었을 때 이상적인 구조를 얻을 수 있다는 것을 확인하였다.

본 연구에서는 바늘형 종결정 코팅 양을 조절함으로써 결정학적으로 b-축 그리고 c-축으로 배향된 모데나이트 제올라이트 분리막을 제조하고 결정학적 배향이 투과증발 에탄올 탈수 거동에 미치는 영향을 고찰하였다. c-축 방향으로 길게 자란 종결정 코팅 양이 증가할수록 b-축 방향에서 c-축 방향으로 성장된 분리막이 얻어졌고, 진화론적 성장 기구에 의해 설명되었다. 8R 단일채널을 갖는 b-축 배향된 분리막은 1000 이상의 선택도와 0.2 kg/m2h의 총 유속을 나타냈다. b-축 방향으로 배향된 분리막이 높은 선택도와 상대적으로 높은 투과도를 보이는 것은 물의 운동역학적 직경이 8R의 직경에 비하여 작기 때문에 물의 이동이 방해되지 않는 반면 에탄올은 상대적으로 방해받기 때문으로 설명되어졌다.

본 연구에서는 DVR 내부 공기유동을 직접 제어하여 CPU의 온도를 낮추기 위한 유동제어 구조물을 제안하였다. 제안된 구조물은 세 개의 얇은 판의 형태로 구성되었으며, DVR 내부의 공기 유동을 포괄적으로 제어하여 CPU의 효율적인 방열을 유도하고자 하였다. DOE와 RSM을 이용한 매개변수 연구기법을 통해 유동제어 구조물의 형상을 최적화하였으며, 해석에는 유한체적방법을 이용한 유체역학 분석 패키지인 FlowVision을 사용하였다. 실제 DVR 기기에서의 실험을 통해 해석 결과를 검증한 결과 CPU의 온도가 16.1℃ 낮아짐을 확인하였다

본 연구에서는 상전이법을 이용하여 P(VDF-co-HFP) 분리막의 구조를 조절하였다. Macrovoid 없는 구조를 얻기 위하여 다양한 조건에서 비용매유도상전이(NIPS) 공법으로 분리막을 제막하였으나 고분자의 낮은 결정화 속도로 인해 macrovoid가 생성된다는 것을 관측하였다. 이를 극복하기 위해 증발유도상전이법(EIPS)과 증기유도상전이법(VIPS)을 도입하였으 며 NIPS공법과 함께 제막되었을 때 이상적인 구조를 얻을 수 있다는 것을 확인하였다.

In this study, TMD(Tuned Mass Damper) is installed in a retractable-roof spatial structure in order to investigate dynamic response characteristics according to mass ratio and installed position of TMD on large spatial structures. The example analytical model is generated based on the Singapore sports hub stadium. Twenty eight analytical models are used to investigate optimal installation position of TMD for the example retractable-roof spatial structure using 4 to 16 TMDs. The mass of one TMD is set up 1% of total mass at the example analytical model. Displacement response ratio of model with TMD is compared with that of base model without TMD. It has been found from numerical simulation that it is more effective to install TMD at the edge of the spatial structure rather than to concentrate the TMD at the center of the spatial structure.