The renewable energy has, currently, been used because of its eco-friendly energy such as no emission gas and less environmental pollution. Fuel cell electric vehicle (FCEV) using polymer electrolyte membrane fuel cell (PEMFC) uses the hydrogen as fuel to obtain the power by electrochemical reaction. The objective of this study is to investigate the flow characteristics of the hydrogen according to entrainment ratio for ejector of FCEV through comparison analysis with the air. As the results, the flow of hydrogen in ejector corresponds to turbulence with Reynold number 18,093. The pressure difference of the hydrogen between primary flow and secondary flow in ejector was about 16 times compared with that of the air. The mean velocity of the hydrogen in ejector outlet was faster about 15 times than the air.

Performance of the hydrogen fuel cell system in a compact special vehicle is mainly influenced by the thermal characteristics of heat release through air flow with electrochemical mechanisms. In this study, numerical analysis has been carried out to investigate air flow and heat transfer characteristics near the fuel cell system for various operating conditions. The cooling characteristics around the radiator system depend on air flow generated by vehicle movement, and the effects of vehicle-induced air flow on the velocity and temperature distributions within the heat release system were examined. These results showed that there are quite complicated air flow around the radiator and fan near the fuel cell system in the vehicle cargo area, and its efficient flow field resulted in cooling performance improvement with driving speed. Hence overall heat release characteristics of the hydrogen fuel cell system are strongly associated with various air flow behavior formed around the compact special vehicle including cargo area.

This research presents a GRNN(General regression neural network) approach for modeling the high temperature deformation flow behavior of 316L stainless steel under 800℃, 900℃ and 1000℃ and strain rates of 0.0002/s, 0.002/s and 0.02/s. There are many machine learning approaches of modeling the hot deformation of metallic alloys. Among them, the neural network approach is one of the most popular. However, the neural network approach takes a relatively long time and effort to compose and optimize the final model. In this research, GRNN is applied to study its applicability for modeling the hot deformation flow stress behavior. The prediction results were studied by calculating various types of error and observing the distribution of prediction error. The predicted results by the GRNN were very accurate and the GRNN was found to be highly applicable to modeling the flow stress of the hot deformation of 316L stainless steel.

This study examines the influence of the number of orifice stages on flow characteristics using Computational Fluid Dynamics (CFD). Transient simulations were conducted with one to four stages under identical boundary conditions, employing the SST turbulence model. The results show that outlet pressure and pressure hunting behaviors are strongly dependent on the stage number. Single- and two-stage models exhibited periodic pressure oscillations, whereas three- and four-stage models demonstrated irregular or stabilized patterns, with the four-stage configuration achieving the lowest pressure hunting. The maximum velocity increased with the number of stages, with peak values observed at the orifice sections. Similarly, eddy viscosity intensified as the number of stages increased, indicating enhanced turbulent mixing. These findings highlight that the number of orifice stages plays a critical role in determining pressure stability and flow behavior, providing useful insights for the optimal design of orifice-based flow control systems.

With the rapid expansion of the electric vehicle (EV) market, the importance of high-efficiency thermal management systems is increasingly being emphasized. The Octo-valve, a key component in Tesla's integrated thermal management system, plays a pivotal role in controlling the flow of refrigerant and coolant to optimize the efficiency of the heat pump system. This study aims to analyze the detailed internal flow characteristics of a single Octo-valve unit and to explore methods for its performance enhancement. For this purpose, an actual Octo-valve was disassembled, and its internal flow paths were modeled in three dimensions using a high-precision 3D scanner. Based on this model, a numerical analysis was conducted using Computational Fluid Dynamics (CFD) to simulate the thermo-fluid phenomena within the valve. Changes in temperature, pressure distribution, and flow velocity were analyzed under various operating conditions and variables, and the resulting pressure drop was quantified. Furthermore, the influence of these internal flow characteristics on the overall system's Coefficient of Performance (COP) and heat transfer efficiency was evaluated. The findings of this research provide a fundamental understanding of the complex fluid dynamics inside the Octo-valve and offer essential baseline data for the design of next-generation, high-efficiency Octo-valves.

Vascular malformations comprise a spectrum of structural anomalies of blood vessels that may present with variable symptoms and clinical behavior. Among these, venous malformations are the most common low-flow lesions and can involve both cutaneous and mucosal tissues. However, intraoral venous malformations, particularly those arising in the buccal mucosa, are uncommon and may be misdiagnosed as other benign oral lesions. In such cases, subtle clinical findings and nonspecific symptoms can delay diagnosis and appropriate management. Imaging modalities, including Doppler ultrasonography and magnetic resonance imaging, are useful for confirming the low-flow nature of the lesion, delineating its extent, and distinguishing it from other vascular anomalies or soft tissue masses. Therapeutic options range from observation to sclerotherapy, laser treatment, or surgical excision, and must be adapted according to lesion size, location, and symptom burden. This report describes a low-flow venous malformation of the buccal mucosa and outlines the clinical, radiologic, and therapeutic considerations relevant to this rare presentation in the head and neck region. By presenting this case and reviewing the pertinent literature, we aim to raise awareness of buccal venous malformations and provide practical guidance for their evaluation and management.

This study aims to provide a basis for selecting the appropriate traffic-flow evaluation indicators by quantitatively analyzing the relative importance of such indicators in mixed traffic environments in which automated vehicles (AVs) and conventional vehicles coexist. As AV technology progresses and its adoption increases, establishing reliable evaluation criteria that accurately reflect the characteristics and performance of traffic systems under transitional conditions is crucial. Thus, approximately 40 domestic and international studies were reviewed in this study, from which 45 evaluation indicators were identified. These indicators were classified into three major categories: mobility, safety, and environment. Five frequently used and representative indicators were selected from each category based on the appearance frequency and relevance. An analytic hierarchy process survey was conducted with a group of transportation experts to derive the relative importance (weights) of both the major categories and individual indicators. The analysis revealed that safety (0.53676) was the most important category, followed by mobility (0.34795) and environment (0.11528). After combining the weights of the categories and sub-indicators, the top three indicators, i.e., time to collision (TTC), time exposed to TTC, and deceleration rate to avoid crashes, appeared to be safety related and associated directly with the collision risk. These findings suggest that, in the early stages of AV deployment, traffic evaluations should prioritize safety considerations over mobility or environmental factors to ensure the successful integration of AVs into existing traffic systems.

본 연구의 목적은 치유 정원을 방문한 이용자를 대상으로 치유 정원의 환경 특성, 몰입경험, 회복 경험 간의 구조적 관계를 검증하는 데 있다. 그리고 환경 특성과 회복 경험 간의 관계에서 몰입경험 의 간접효과를 실증적으로 규명하고자 한다. 연구 목적을 달성하기 위해 치유 정원에 방문한 경험 이 있는 성인 남,녀를 모집단으로 하여 비확률 표본 추출 방법(Non-probability sampling method) 중 편의 표본 추출 방법(Convenience sampling method)으로 설문조사를 하였다. 배포한 설문지 중 283명의 설문지를 수집하였으며, 이 중 연구 목적에 맞지 않는다고 판단하는 33부의 설문지를 제외한 250부가 최종 분석에 사용되었다. 분석 방법은 SPSS 25.0, Amos 25.0프로그램 을 이용하여 빈도분석, 측정모형분석, 신뢰도 검증, 상관관계분석, 구조모형 분석, Bootstrapping 방법을 이용한 매개효과 분석을 하였다. 이에 따른 연구 결과는 다음과 같다. 첫째, 치유 정원의 환경 특성은 회복 경험에 통계적으로 유의한 영향을 미치는 것으로 나타났다. 둘째, 치유 정원에서 의 몰입경험은 회복 경험에 통계적으로 유의한 영향을 미치는 것으로 나타났다. 셋째, 치유 정원의 환경 특성은 몰입경험에 통계적으로 유의한 영향을 미치는 것으로 나타났다. 넷째, 환경 특성과 회복 경험 간의 관계에서 몰입경험은 매개효과가 있는 것으로 나타났다.

본 연구에서는 과불화 알킬 사슬이 도입된 산화 그래핀(perfluoroalkyl-grafted graphene oxide, FGO)을 합성하고, 이를 과불소화계 고분자인 나피온(Nafion)에 복합화하여 바나듐 레독스 흐름 전지(vanadium redox flow battery, VRFB)용 이 온 교환 막을 개발하고자 하였다. FGO는 염기성 촉매 하에서 카르복실산기를 함유한 폴리(헥사플루오로프로필렌 옥사이드) (157 FSL, DuPont)의 카르복실산기와 GO의 에폭시기 간 개환 에스터화 반응을 통해 합성하였다. 합성된 FGO를 Nafion 기 지체에 함량을 달리하여 첨가한 복합막(N/FGO_X)을 제조하고, 함수율, 체적 안정성, 수소 이온 전도도, 바나듐 이온 투과도 및 셀 성능을 평가하였다. N/FGO 복합막은 Nafion 단일막 대비 낮은 함수율과 체적 변화율을 보였으며, FGO의 물리적 차단 효과에 의해 바나듐 이온 투과도가 감소하면서도 수소 이온 전도도를 유지하여 우수한 이온 선택도를 나타내었다. VRFB 단 위 셀 평가 결과, FGO가 도입된 복합막은 Nafion 단일막을 적용한 셀 대비 높은 방전 용량, 쿨롱 효율 및 에너지 효율을 유 지하였다.

The purpose of this study is to identify the flow resistance characteristics of the trawl net according to the towing speed of the vessel using two trawl nets designed and manufactured based on 2,000 HP. The trawl net consists of wings, bag and cod-end part, two types with wall area  of 747 m 2 (Sae Dong Baek) and 1,262 m 2 (Dong Baek) with differences in the size of the trawl net. The result of sea experiments are as follows: the flow resistance of trawl net  at the flow velocity  = 1 m/s or higher is affected by the difference in the composition of the cod-end rather than the wing or bag part of the Sae Dong Baek´s trawl net, Dong Baek´s the cod-end part has a  ratio value of 1.19, compared to Sae Dong Baek´s trawl net with a size of 120 m, and Dong Baek´s trawl net is small at 60 mm. Therefore, the water entering into the net cannot easily pass, which is considered to be a factor that increases resistance at the cod-end part. In the result of the experiment, it was found that  decreases exponentially when  increases which makes  . The constant  values when  = 1 m/s were 6.72 and 3.75, and  values were 1.14 and 0.94, showing a difference between the two nets as the flow velocity  increased. The height at the mouth of bottom trawl net decreases exponentially as the current velocity  increases; such height given by   where the constant  and  values are 0.85 for the increase in the flow velocity  and the  value when =1 m/s is 4.35. Therefore, this study investigated the flow resistance characteristics of trawl net at sea. It was possible to obtain more reliable information than previous studies by using a real fishing vessel with advanced underwater measurement devices. As a result, it was possible to analyze the underwater shape change of trawl net and the resulting flow resistance characteristics more quantitatively.

In this study, for the design of the impeller and volute casing shape of the water pump for flood prevention, performance was predicted through numerical analysis to secure the theoretical power and hydraulic efficiency of the front well at the discharge well 300m3/h, which is the target design specification, and the flow characteristics of each flow rate were checked and verified. Through the results of this flow analysis, it was possible to secure the basic shape design of the impeller and volute casing of the water pump for flood prevention. In the future, we will perform an interpretation to confirm structural safety according to shape and material.

Active electronically scanned array (AESA) multi-function radars (MFRs) comprise numerous transmit/receive modules (TRMs) whose maximum temperature and temperature uniformity must be tightly controlled. This study proposes a new liquid-cooling-plate flow-channel design for an X-band AESA MFR: a two-layer straight channel incorporating multiple fins irregularly spaced along the flow channel. The proposed design (Type-4) is compared with three baseline channel designs. At the same coolant flow rate, Type-4 reduces the TRM maximum temperature by 28.2 K and the maximum inter-module temperature difference by 19.7 K relative to Type-1. However, the pressure drop increases by 726% because of the added internal surfaces and fins which are flow obstructions. A comprehensive thermo-hydraulic comparison, including pumping power criteria, is conducted over multiple flow-rate conditions. Overall performance was highest for Type-4, followed by Type-2, Type-3, and Type-1. When designs achieve similar maximum temperature and temperature difference with various coolant flowrate condition, Type-2 requires 83.6% less pumping power than Type-1, and Type-4 requires 33.8% less pumping power than Type-2.

This study investigates the flow resistance and heat transfer characteristics of a fin-and-tube heat exchanger, applied to a water-cooled thermal management system designed for a cabinet-mounted high-performance computer operating aboard naval vessels. The analysis was conducted through both experimental and numerical approaches, focusing on the evaluation of heat transfer performance (j factor) and flow resistance (f factor) under varying air flow rates, while maintaining a fixed fin geometry and arrangement. Particular emphasis was placed on assessing the variation of the j factor along the total length of the heat exchanger to understand the impact of exchanger length on thermal performance. In the numerical analysis, instead of modeling the entire heat exchanger, a representative repeated unit composed of a single fin and twelve connected tubes was simulated. The outlet temperature from each tube segment was sequentially used as the inlet condition for the subsequent segment. This methodology significantly enhances computational efficiency while providing reliable predictions of progressive thermal characteristics along the flow path.

수치 모의 실험에서 보여주는 블랙홀 주변의 강착원반은 유입기체의 조건에 따라서 때로는 안정적으로 때로는 불안정적으로 나타난다. 이 연구에서는 여러 가지 다른 종류의 해석적인 해를 가진 기체들 중 충격파의 특성을 잘 보 여주는 점성을 가진 기체에 대하여 Lagrangian TVD+remap 코드를 사용하여 2차원적인 원통좌표계에서 수치모의 실험 을 시행하였다. 수치모의 실험은 점성이 0.01을 가진 점성 이류가스 (viscously advected flow)가 400rg인 바깥쪽 경계 면 (outer boundary)에서 유입되었다. 유입된 기체는 블랙홀 가까이에서는 해석적인 해와 잘 일치하였으나 100rg 부근 에서 나타나는 충격파의 위치는 시간에 따라 변화함을 보여주었다. 이 기체에 대한 해석적인 해에서는 100rg 부근에서 특정 각운동량 (specific angular momentum)이 역전되는 곳이 존재하는데, 수치모의 실험에서는 특정 각운동량이 역전 되고 있는 지점에서 충격파의 존재가 관측되었다. 이 충격파는 블랙홀에 의하여 흡수되는 질량 부착율이 증가할 때, 안 쪽으로 진행하면서, 때로는 안쪽에서 새로운 충격파를 생성하기도 하였으며, 안쪽과 바깥쪽의 충격파가 충돌하는 현상 을 보이기도 하였다. 평균 질량 부착율은 유입 질량의 20-30%로 나타나며, 가끔씩 평균질량의 2-3배 되는 질량 부착율 을 보여주기도 하고, 해석적인 해에서 예측하는 것처럼 z-축방향으로의 제트 흐름을 보이기도 하였다.