• Current Photovoltaic Research
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• v.10 no.1
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• pp.16-22
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• 2022

The long-term stability of PSCs against visual and UV light, moisture, electrical bias and high temperature is an important issue for commercialization. In particular, since the operation temperature of solar cell can rise above 85℃, a study on thermal stability is required. In this study, the cause of thermal-induced degradation of PSCs was investigated using the SCAPS-1D simulation tool. First, PSCs of TiO₂/CH₃NH₃PbI₃/Spiro-OMeTAD/Au structure were exposed to a constant temperature of 85℃ to observe changes in conversion efficiency and quantum efficiency. Because the EQE reduction above 500 nm was remarkable, we simulated PSCs performance as a function of lifetime, doping density of perovskite and spiro-OMeTAD. Consequently, the main cause of thermal-induced degradation is considered to be the change in the perovskite doping concentration and lifetime due to ion migration of perovskite.

• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.647-661
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• 2023

It is recognized that the installation of energy dissipation devices, such as the tuned mass damper (TMD), decreases the dynamic response of structures, however, the best parameters of each device persist hard to determine. Unlike many works that perform only a deterministic optimization, this work proposes a complete methodology to minimize the dynamic response of footbridges by optimizing the parameters of multiple tuned mass dampers (MTMD) taking into account uncertainties present in the parameters of the structure and also of the human excitation. For application purposes, a steel footbridge, based on a real structure, is studied. Three different scenarios for the MTMD are simulated. The proposed robust optimization problem is solved via the Circle-Inspired Optimization Algorithm (CIOA), a novel and efficient metaheuristic algorithm recently developed by the authors. The objective function is to minimize the mean maximum vertical displacement of the footbridge, whereas the design variables are the stiffness and damping constants of the MTMD. The results showed the excellent capacity of the proposed methodology, reducing the mean maximum vertical displacement by more than 36% and in a computational time about 9% less than using a classical genetic algorithm. The results obtained by the proposed methodology are also compared with results obtained through traditional TMD design methods, showing again the best performance of the proposed optimization method. Finally, an analysis of the maximum vertical acceleration showed a reduction of more than 91% for the three scenarios, leading the footbridge to acceleration values below the recommended comfort limits. Hence, the proposed methodology could be employed to optimize MTMD, improving the design of footbridges.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.539-549
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• 2006

The performance of a pontoon-type floating breakwater (FB) is investigated numerically with the use of a second-order time domain model. The model has been developed based on potential theory, perturbation theory and boundary element method. This study is focused on the effects of weakly nonlinear wave on the hydrodynamic characteristics of the FB. Hydrodynamic forces, motion responses, surface elevation, and wave transmission coefficient around the floating breakwater are evaluated for various wave and geometric parameters. It is shown that the second-order wave component is of significant importance in calculating magnitudes of the hydrodynamic forces, mooring forces and the maximum response of a structure. The weak non-linearity of incident waves, however, can have little influence on the efficiency of the FB. From numerical simulations, the ratio of draft and depth, the relationship of wave number and width are presented for providing an effective means of reducing wave energy.

• Advances in nano research
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• v.15 no.5
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• pp.467-484
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• 2023

Despite the significant features of fiber-reinforced cementitious composites (FRCCs), including better mechanical, fractural, and durability performance, their high content of cement has restricted their use in the construction industry. Although ground granulated blast furnace slag (GGBFS) is considered the main supplementary cementitious material, its slow pozzolanic reaction stands against its application. The addition of nano-sized mineral modifiers, including nano-silica (NS), is an alternative to address the drawbacks of using GGBFS. The main object of this empirical and numerical research is to examine the effect of NS on the strain-hardening behavior of cementitious composites; ten mixes were designed, and five levels of NS were considered. This study proposes a new method, using a four-point bending test to assess the use of nano-silica (NS) on the flexural behavior, first cracking strength, fracture energy, and micromechanical parameters including interfacial friction bond strength and maximum bridging stress. Digital image correlation (DIC) was used for monitoring the initiation and propagation of the cracks. In addition, to attain a deep comprehension of fiber/matrix interaction, scanning electron microscope (SEM) analysis was used. It was discovered that using nano-silica (NS) in cementitious materials results in an enhancement in the matrix toughness, which prevents multiple cracking and, therefore, strain-hardening. In addition, adding NS enhanced the interfacial transition zone between matrix and fiber, leading to a higher interfacial friction bond strength, which helps multiple cracking in the composite due to the hydrophobic nature of polypropylene (PP) fibers. The findings of this research provide insight into finding the optimum percent of NS in which both ductility and high tensile strength of the composites would be satisfied. As a concluding remark, a new criterion is proposed, showing that the optimum value of nano-silica is 2%. The findings and proposed method of this study can facilitate the design and utilization of green cementitious composites in structures.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.1-8
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• 2024

This paper employs stochastic processing techniques to analyze explosion risks in plant facilities based on explosion return periods. Release probability is calculated using data from the Health and Safety Executive (HSE), along with annual leakage frequency per plant provided by DNV. Ignition probability, derived from various researchers' findings, is then considered to calculate the explosion return period based on the release quantity. The explosion risk is assessed by examining the volume, radius, and blast load of the vapor cloud, taking into account the calculated explosion return period. The reference distance for the design blast load model is determined by comparing and analyzing the vapor cloud radius according to the return period, historical vapor cloud explosion cases, and blast-resistant design guidelines. Utilizing the multi-energy method, the blast load range corresponding to the explosion return period is presented. The proposed return period serves as a standard for the design blast load model, established through a comparative analysis of vapor cloud explosion cases and blast-resistant design guidelines. The outcomes of this study contribute to the development of a performance-based blast-resistant design framework for plant facilities.

• Design & Manufacturing
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• v.17 no.3
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• pp.15-20
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• 2023

In the fine blanking process, which is a press operation known for producing parts with narrow clearances and high precision through the application of high pressure, die roll often occurs during the shearing process when the punch penetrates the material. This die roll phenomenon can significantly reduce the functional surface of the parts, leading to decreased product performance, strength, and fatigue life. In this research, we conducted an in-depth analysis of the factors influencing die roll in the curvature area of the fine blanking process and identified its root causes. Subsequently, we designed and experimentally verified a die roll reduction process specifically tailored for the door latch manufacturing process. Our findings indicate that die roll tends to increase as the curvature radius decreases, primarily due to the heightened bending moment resulting from reduced shape width-length. Additionally, die roll is triggered by the absorption of initial punch energy by scrap material during the early shearing phase, resulting in lower speed compared to the product area. To mitigate the occurrence of die roll, we strategically selected the Shaving process and carefully determined the shaving direction and clearance area length. Our experiments demonstrated a promising trend of up to 75% reduction in die roll when applying the Shaving process in the opposite direction of pre-cutting, with the minimum die roll observed at a clearance area length of 0.2 mm. Furthermore, we successfully implemented this approach in the production of door latch products, confirming a significant reduction in die roll. This research contributes valuable insights and practical solutions for addressing die roll issues in fine blanking processes.

• Animal Bioscience
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• v.37 no.2_spc
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• pp.370-384
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• 2024

Rumen microbiota play a central role in the digestive process of ruminants. Their remarkable ability to break down complex plant fibers and proteins, converting them into essential organic compounds that provide animals with energy and nutrition. Research on rumen microbiota not only contributes to improving animal production performance and enhancing feed utilization efficiency but also holds the potential to reduce methane emissions and environmental impact. Nevertheless, studies on rumen microbiota face numerous challenges, including complexity, difficulties in cultivation, and obstacles in functional analysis. This review provides an overview of microbial species involved in the degradation of macromolecules, the fermentation processes, and methane production in the rumen, all based on cultivation methods. Additionally, the review introduces the applications, advantages, and limitations of emerging omics technologies such as metagenomics, meta-transcriptomics, metaproteomics, and metabolomics, in investigating the functionality of rumen microbiota. Finally, the article offers a forward-looking perspective on the new horizons and technologies in the field of rumen microbiota functional research. These emerging technologies, with continuous refinement and mutual complementation, have deepened our understanding of rumen microbiota functionality, thereby enabling effective manipulation of the rumen microbial community.

• Earthquakes and Structures
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• v.27 no.1
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• pp.17-29
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• 2024

The traditional double story isolated structure is a derivative of the base isolated and inter-story isolated structures, while the new double story isolated structure represents a novel variation derived from the traditional double story isolated structure. In order to investigate the seismic response of the new double story isolated structure, a comprehensive structural model was developed. Concurrently, models for the basic fixed, base isolated, inter-story isolated, and traditional double story isolated structures were also established for comparative analysis. The nonlinear dynamic time-history response of the new double story isolated structure under rare earthquake excitations was analyzed. The findings of the study reveal that, in comparison to the basic fixed structure, the new double story isolated structure exhibits superior performance across all evaluated aspects. Furthermore, when compared to the base isolated and inter-story isolated structures, the new double story isolated structure demonstrates significant reductions in inter-story shear force, top acceleration, and inter-frame displacement. The horizontal displacement of the new double story isolated structure is primarily localized within the two isolation layers, effectively dissipating the majority of input seismic energy. In contrast to the traditional double story isolated structure, the new design minimizes displacements within the inter-isolation layer situated in the central part of the frame, as well as mitigates the overturning forces acting on the lower frame column. Consequently, this design ensures the structural integrity of the core tube, thereby preventing potential collapse and structural damage.

• Archives of Metallurgy and Materials
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• v.64 no.2
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• pp.551-557
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• 2019

The dispersion of nanoparticles in the host matrix is a novel approach to enhance the thermoelectric performance. In this work, we incorporate the TiC (x = 0, 1 and 2 wt.%) nanoparticles into a p-type Bi_0.5Sb_1.5Te₃ matrix, and their effects on microstructure and thermoelectric properties were systematically investigated. The existence of TiC contents in a base matrix was confirmed by energy dispersive X-ray spectroscopy analysis. The grain size decreases with increasing the addition of TiC content due to grain boundary hardening where the dispersed nanoparticles acted as pinning points in the entire matrix. The electrical conductivity significantly decreased and the Seebeck coefficient was slightly enhanced, which attributes to the decrease in carrier concentration by the addition of TiC content. Meanwhile, the lowest thermal conductivity of 0.97 W/mK for the 2 wt.% TiC nanocomposite sample, which is ~16% lower than 0 wt.% TiC sample. The maximum figure of merit of 0.90 was obtained at 350 K for the 0 wt.% TiC sample due to high electrical conductivity. Moreover, the Vickers hardness was improved with increase the addition of TiC contents.

• Advances in materials Research
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• v.13 no.5
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• pp.391-416
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• 2024

Hybrid composite materials are widely used in various load-bearing structural components of micro - mini UAVs. However, the design of thin laminates for better impact resistance remains a challenge, despite the strong demand for lightweight structures. This work aims to assess the low-velocity impact (LVI) behaviour of thin quasi-isotropic woven carbon/ aramid epoxy hybrid laminates using experimental and numerical techniques. Drop tower impact test with 10 J and 15 J impact energies is performed on carbon/epoxy laminates having aramid layers at different sequences and locations. The impact behaviour is experimentally evaluated using force-time, force-deformation, and energy-time histories considering delamination threshold load, peak load, and laminate deflection. Ultrasonic C-scan is performed on the post-impact samples to analyse the insidious damage profile at different impact energies. The experimental data is further utilized to numerically simulate LVI behaviour by employing the representative volume element model. The numerical results are in good agreement with the experimental data. Numerical and experimental approach predicts that the hybrid laminates with aramid layers at both impact and non-impact sides of the laminate exhibits significant improvement in the overall impact behaviour by having a subcritical damage morphology compared to carbon/epoxy laminate. A combined numerical-experimental approach is proposed for evaluating the effective impact performance.