https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/185 2026-07-24T09:20:50Z https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/218037 Title: Key factor governing transient maldistribution in proton exchange membrane fuel cells: A numerical study on decoupling modeling framework and sorption rate asymmetry Authors: Lee, Sumin; Sohn, Young-Jun; Choi, Yoon-Young; Lim, In Seop; Um, Sukkee; Oh, Hwanyeong Abstract: Accurate transient modeling of proton exchange membrane fuel cells (PEMFCs) requires careful treatment of ionomer water sorption and desorption kinetics. To address uncertainties in modeling approaches, this study utilizes a transient, three-dimensional, two-phase, non-isothermal model under 50% relative humidity conditions. We first compared widely used representative sorption-rate models, which differ in modeling frameworks (equation-based vs. constant-rate) and sorption-rate coefficient symmetry (symmetric vs. asymmetric). Their intertwined characteristics were then systematically decoupled to assess the isolated effect of each factor on transient dynamics. Within the load-step protocols and operating conditions investigated in this study, the modeling framework has a secondary influence on predicted transient behaviors and spatial distributions, as a constant-rate model with matched time-averaged coefficients captures the main trends of the equation-based results. In contrast, sorption-rate coefficient symmetry plays a decisive role. Desorption-dominant asymmetry in the sorption-rate coefficients causes severe local dehydration and a redistribution of current density during galvanostatic transients. Among water phases, the ionomer water content shows the greatest sensitivity to the sorption-rate model, with the most direct link to the current density distribution. This 3D analysis provides guidance for future modeling by showing how sorption-rate model selection and coefficient parameterization influence the prediction of transient performance and spatial nonuniformity, which are not observable in lower-dimensional models. 2027-01-01T00:00:00Z https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/213325 Title: A two-phase topology optimization method for manufacturable functionally-graded lattice structures with casting process Authors: Yi, Bing; Liu, Long; Wang, Tianci; Peng, Xiang; Yoon, Gil-Ho Abstract: Topology optimization often yields intricate truss-like structures that are challenging to fabricate using conventional manufacturing methods. To deal with this issue, this paper proposes a two-phase topology optimization method to enhance the manufacturability of functionally-graded lattice structures with the casting process. Specifically, the minimal length scales of two phases, including void and solid phases are proposed to exactly align with the manufacturing constraints of the final product and its mold. Additionally, a penalty function is employed to eliminate grey elements, ensuring a clear, easily manufacturable solution for both the cast product and its mold. Finally, the two-phase-based topology optimization of both conventional continuous structures and functionally-graded lattice structures is formulated, and the product and its mold are optimized simultaneously via the Method of Moving Asymptotes (MMA). Numerical examples of both the conventional SIMP method and the integration of functionally-graded lattice structures are used to demonstrate the effectiveness of the proposed method in simultaneously optimizing both the product and casting. To validate the approach, a functionally-graded lattice structure was successfully cast using aluminum alloy, confirming the practical applicability of the method. 2026-12-01T00:00:00Z https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/219164 Title: Strategic selection of multi-parametric laser settings and clinical endpoints in dermatology: an engineering-to-clinical review Authors: Park, Soobeen; Hyeon, Jihee; So, Hongyun Abstract: Selective photothermolysis, which enables precise targeting of melanin, hemoglobin, and water, is the foundation for modern dermatologic laser therapy. This review bridges laser physics with clinical practice by organizing systems on the basis of spectral domain and indication: Q-switched and picosecond lasers for tattoos and lentigines; pulsed-dye and long-pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers for vascular lesions; alexandrite and diode lasers for hair removal; and fractional ablative (CO₂, erbium-doped yttrium aluminum garnet [Er:YAG]) and non-ablative platforms for scar revision and rejuvenation. Unlike conventional textbook reviews that merely list device specifications, we specifically define how to dynamically adjust comprehensive parameters not just wavelength, but also pulse duration, fluence, and spot size—in direct response to immediate clinical endpoints observed during treatment. We delineated the selection of parameters—wavelength, pulse duration, fluence, and spot size—in relation to the Fitzpatrick skin type, focusing on cooling, treatment endpoints, and recovery. Current evidence regarding efficacy, recurrence, and complications has been synthesized, and the device parameters have been linked to thermal relaxation and Arrhenius injury kinetics to inform safer evidence-based algorithms and multimodal treatment strategies. 2026-12-01T00:00:00Z https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/213315 Title: Improvement of natural convection heat dissipation of a conventional pin-fin heat sink by applying a helical wire spring Authors: Kang, Hyeon-Min; Ko, Jae-Yong; Zulkifli, Noraina Zulaikha Awang; Yusof, Nur Ain Syafiqah; Yook, Se-Jin Abstract: Effective heat dissipation of electronic devices including high-power light-emitting diodes (LEDs) is essential in applications requiring both compact size and high performance. In such environments, passive cooling technologies providing high heat dissipation with simple structures are particularly desirable. This study proposes a new method to enhance the cooling performance of conventional pin-fin heat sinks by applying a spring-shaped wire structure around the outer surfaces of the fins. Aluminum 6061 or SAC305 wire was formed into a helical spring and wrapped around the fins without altering the original heat sink geometry, enabling attachment to existing products. The spring structure increases the effective surface area and guides airflow between fins, thereby enhancing free convection heat transfer. Experiments and numerical simulations were conducted to evaluate the thermal performance of the proposed design. For the reference heat sink without springs, a simple rising buoyant flow developed between the fins. In contrast, the spring-equipped heat sink induced more complex flow paths along the spring geometry, promoting enhanced air circulation. This resulted in more uniform heat distribution and a reduction in overall thermal resistance. Comparative analysis under different installation angles showed that the aluminum-spring-applied heat sink achieved a maximum thermal-resistance reduction of 11.72% relative to the reference model, demonstrating consistent performance improvement under various orientations. These results show that the simple addition of a spring structure can significantly improve the natural-convection cooling performance of conventional heat sinks, indicating its potential as a scalable and feasible thermal management solution for high-power electronic devices and LED lighting systems. 2026-11-01T00:00:00Z