ACTIVELY TRANSLATING A REAR DIFFUSER DEVICE FOR THE AERODYNAMIC DRAG REDUCTION OF A PASSENGER CAR

Kang, S.O.,Jun, S.O.,Park, H.I.,Song, K.S.,Kee, J.D.,Kim, K.H.,Lee, D.H. 한국자동차공학회 2012 International journal of automotive technology Vol.13 No.4

This research aims to develop an actively translating rear diffuser device to reduce the aerodynamic drag experienced by passenger cars. One of the features of the device is that it is ordinarily hidden under the rear bumper but slips out backward only under high-speed driving conditions. In this study, a movable arc-shaped semi-diffuser device, round in form, is designed to maintain the streamlined automobile's rear underbody configuration. The device is installed in the rear bumper section of a passenger car. Seven types of rear diffuser devices whose positions and protrusive lengths and widths are different (with the basic shape being identical) were installed, and Computational Fluid Dynamics (CFD) analyses were performed under moving ground and rotating wheel conditions. The main purpose of this study is to explain the aerodynamic drag reduction mechanism of a passenger car cruising at high speed via an actively translating rear diffuser device. The base pressure of the passenger car is increased by deploying the rear diffuser device, which then prevents the low-pressure air coming through the underbody from directly soaring up to the rear surface of the trunk. At the same time, the device generates a diffusing process that lowers the velocity but raises the pressure of the underbody flow, bringing about aerodynamic drag reduction. Finally, the automobile's aerodynamic drag is reduced by an average of more than 4%, which helps to improve the constant speed fuel efficiency by approximately 2% at a range of driving speeds exceeding 70 km/h.

COMPARATIVE INVESTIGATION ON THE AERODYNAMIC EFFECTS OF COMBINED USE OF UNDERBODY DRAG REDUCTION DEVICES APPLIED TO REAL SEDAN

조준호,김태경,김규홍,이관중 한국자동차공학회 2017 International journal of automotive technology Vol.18 No.6

To reduce the aerodynamic drag, the performance of the underbody aerodynamic drag reduction devices was evaluated based on the actual shape of a sedan-type vehicle. An undercover, under-fin, and side air dam were used as the underbody aerodynamic drag reduction devices. In addition, the effects of the interactions based on the combination of the aerodynamic drag reduction devices were investigated. A commercial sedan-type vehicle was selected as a reference model and its shape was modeled in detail. Aerodynamic drag was analyzed by computational fluid dynamics at a general driving speed on highway of 120 km/h. The undercover reduced the slipstream area through the attenuation of the longitudinal vortex pair by enhancing the up-wash of underflow, thereby reducing the aerodynamic drag by 8.4 %. The under-fin and side air dam showed no reduction in aerodynamic drag when they were solely attached to the actual complex shape of the underbody. Simple aggregation of the effects of aerodynamic drag reduction by the individual device did not provide the accurate performance of the combined aerodynamic drag reduction devices. An additional aerodynamic drag reduction of 2.1 % on average was obtained compared to the expected drag reduction, which was due to the synergy effect of the combination.

Modest Effects of Neurofeedback-Assisted Meditation Using a Wearable Device on Stress Reduction: A Randomized, Double-Blind, and Controlled Study

Lee Eunyoung,Hong Jung Kyung,Choi Hayun,Yoon In-Young 대한의학회 2024 Journal of Korean medical science Vol.39 No.9

Background: To evaluate the therapeutic effectiveness and safety of a neurofeedback wearable device for stress reduction. Methods: A randomized, double-blind, controlled study was designed. Participants had psychological stress with depression or sleep disturbances. They practiced either neurofeedback-assisted meditation (n = 20; female, 15 [75.0%]; age, 49.40 ± 11.76 years) or neurofeedback non-assisted meditation (n = 18; female, 11 [61.1%]; age, 48.67 ± 12.90 years) for 12 minutes twice a day for two weeks. Outcome variables were self-reported questionnaires, including the Korean version of the Perceived Stress Scale, Beck Depression Inventory-II, Insomnia Severity Index, Pittsburgh Sleep Quality Index, and State Trait Anxiety Index, quantitative electroencephalography (qEEG), and blood tests. Satisfaction with device use was measured at the final visit. Results: The experimental group had a significant change in PSS score after two weeks of intervention compared with the control group (6.45 ± 0.95 vs. 3.00 ± 5.54, P = 0.037). State anxiety tended to have a greater effect in the experimental group than in the control group (P = 0.078). Depressive mood and sleep also improved in each group, with no significant difference between the two groups. There were no significant differences in stress-related physiological parameters, such as stress hormones or qEEG, between the two groups. Subjective device satisfaction was significantly higher in the experimental group than in the control group (P = 0.008). Conclusion: Neurofeedback-assisted meditation using a wearable device can help improve subjective stress reduction compared with non-assisted meditation. These results support neurofeedback as an effective adjunct to meditation for relieving stress.

선박용 디젤엔진의 미세먼지저감 장치에 다공판과 믹서의 장착이 미치는 영향에 대한 수치해석적 연구

윤병규,조상현,류영현 해양환경안전학회 2019 해양환경안전학회지 Vol.25 No.7

본 논문에서는 선박용 디젤엔진의 미세먼지저감 장치에 장착된 다공판 및 믹서의 형상과 배치에 따른 압력강하와 유동균일도 특성에 대한 연구를 진행하였다. 미세먼지저감 장치에 장착된 다공판 및 믹서는 미세먼지저감 장치 내의 배출가스 및 산화/환원제의 유동균일도를 높여 배출가스 저감 성능을 높이는 긍정적인 효과와 함께 시스템의 배압을 상승시키는 부정적인 효과도 동시에 지니고 있다. 본 연구에서는 5개의 다공판, 1개의 믹서를 Case 별로 조합하여 6개의 사양에 대해서 유동해석을 통해 각각 유동균일도 및 압력 강하를 계산하였으며, 최적의 다공판 및 믹서의 형상과 배치를 선정하였다. This study presents the characteristics of a pressure drop and uniformity index for a particulate matter reduction device with a perforated plate and mixer for marine diesel engines. The perforated plate and mixer equipped on the particulate matter reduction device induce an increase of exhaust gas reduction performance by increasing the uniformity index. Whereas, the perforated plate induces pressure drop increases in the particulate matter reduction device. Therefore to calculate the effect of the uniformity index and pressure drop of the perforated plates and mixer, this study combines several cases using five types of perforated plates and one type of mixer. Consequently, these results were analyzed to determine the optimized type and position of the perforated plate and mixer.

고속철도용 방음시설 보완을 위한 소음저감장치의 현장적용에 관한 연구

조영규,장강석,정찬묵,어성욱 대한환경공학회 2019 대한환경공학회지 Vol.41 No.4

Recently, the speed of high-speed railway has been rapidly increased with the development of high-speed train design and operating technology. This causes a lot of complaints related the environmental noise in residential areas near the high-speed railway. Also the civil complaints about environmental noise of high-speed railway are also increasing continuously. In this study, we was surveyed the current state of soundproofing facilities for high-speed railway and general railway in Korea, and conducted long-term monitoring of the noise reduction device installed to supplement soundproofing facilities. And in order to evaluate the field application performance through long-term monitoring, domestic and overseas evaluation methods were analyzed. Through such research, we have presented the two types method to verify the performance of the newly developed noise reduction device. One is to evaluate before and after installation, and the other is the evaluation method which measures installed and not installed site at the same time. The results of monitoring using these evaluation methods according to the season for 5 years, it has been confirmed that performance of the noise reduction device is consistently above 3 dB. 고속열차의 설계 및 운행기술이 발전하면서 고속철도의 운행속도가 빠르게 증속되고 있다. 반면 증속 시 발생하는소음으로 인해 고속철도 연변의 주거지역에서는 많은 소음문제가 발생하고 있으며, 고속철도 소음에 대한 민원도 지속적인증가추세에 있다. 본 연구에서는 국내 고속철도 및 일반철도에 대한 방음시설 현황을 조사하고, 방음시설 성능보완을 위해설치된 소음저감장치에 대한 장기모니터링을 수행하였다. 또한 소음저감장치의 현장적용성능을 평가하기 위한 국내외 평가방법을 분석하였다. 이와 같이 평가방법에 대한 조사 후 두 가지 평가방법을 제시하였다. 첫 번째 평가방법은 설치 전과 설치 후에 측정하여 평가방법이고, 다른 하나는 설치와 미설치 구간을 동시에 측정하여 평가하는 방법으로 장기모니터링에 적합한 평가방법이다. 한편 이 두 가지 평가방법을 이용하여 소음저감장치에 대한 성능을 분석한 결과, 개발된 소음저감장치는5년 동안 시기나 날씨에 관계없이 지속적으로 3 dB 이상의 소음저감이 되는 것을 검증하였다.

Combined Effect of Catholyte Gap and Cell Voltage on Syngas Ratio in Continuous CO₂/H₂O Co-electrolysis

Ha, Min Gwan,Na, Youngseung,Park, Hee Young,Kim, Hyoung-Juhn,Song, Juhun,Yoo, Sung Jong,Kim, Yong-Tae,Park, Hyun S.,Jang, Jong Hyun The Korean Electrochemical Society 2021 Journal of electrochemical science and technology Vol.12 No.4

Electrochemical devices are constructed for continuous syngas (CO + H₂) production with controlled selectivity between CO₂ and proton reduction reactions. The ratio of CO to H₂, or the faradaic efficiency toward CO generation, was mechanically manipulated by adjusting the space volume between the cathode and the polymer gas separator in the device. In particular, the area added between the cathode and the ion-conducting polymer using 0.5 M KHCO₃ catholyte regulated the solution acidity and proton reduction kinetics in the flow cell. The faradaic efficiency of CO production was controlled as a function of the distance between the polymer separator and cathode in addition to that manipulated by the electrode potential. Further, the electrochemical CO₂ reduction device using Au NPs presented a stable operation for more than 23 h at different H₂:CO production levels, demonstrating the functional stability of the flow cell utilizing the mechanical variable as an important operational factor.

Carbothermal process-derived porous N-doped carbon for flexible energy storage: Influence of carbon surface area and conductivity

Sawant, Sandesh Y.,Cho, Moo Hwan,Kang, Misook,Han, Thi Hiep Elsevier 2019 Chemical engineering journal Vol.378 No.-

<P><B>Abstract</B></P> <P>A simple and scalable method to synthesize N-doped carbon (NC) based on a carbothermal reduction of a ZnO/carbon composite (ZCC) obtained from the decomposition of a zinc aniline nitrate complex is reported. The present study examined the effects of the structural characteristics of NC, such as electrical conductivity and surface area, more precisely without altering the other structural features of NC. A carbothermal reduction of ZCC allowed the production of hierarchically porous NC with a low sheet resistance of 0.432 kΩ □<SUP>−1</SUP> without any post-treatment with Zn nanorods as a valuable byproduct. The resulting NC exhibited ultra-high stability and rate capability, i.e., 100% stability after 200,000 cycles up to 300 A g<SUP>−1</SUP> with a high capacitance of 229 F g<SUP>−1</SUP> at 0.5 A g<SUP>−1</SUP>. The 288% increase in surface area with a similar % contribution from micro and mesopores and similar electrical conductivity increased the electrochemical charge storage capacity of NC by 266%. Similarly, NC materials possessing a similar surface area but a large difference in electrical conductivity resulted in a 1539% difference in charge storage capacity. Enhancement of both the surface area and electrical conductivity improved the capacitance of NC drastically to 4098% higher than the base product. A prototype flexible solid-state supercapacitor fabricated from the obtained NC delivered a very high areal capacitance of 363.6 mF cm<SUP>−2</SUP> (at 0.5 mA cm<SUP>−2</SUP>) with ultra-high stability (82%) even after 70,000 cycles (at 25 mA cm<SUP>−2</SUP>).</P> <P><B>Highlights</B></P> <P> <UL> <LI> N-doped carbon (NC) with tunable properties is obtained using carbothermal method. </LI> <LI> Simultaneous production Zn nanotubes results in waste-free approach. </LI> <LI> Charge storage capacity of NC precisely studied against conductivity/surface area. </LI> <LI> High capacitance of 229 F/g with exceptional rate capability is observed for NC. </LI> <LI> Ultra-high stability is retained with flexible prototype solid state device. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Harmonic Current Reduction Analysis of Traditional PI and Enhanced FoPID Controller-Based MSALC

Muralikrishnan Gopalakrishnan,Mohanty Nalin Kant 대한전기학회 2021 Journal of Electrical Engineering & Technology Vol.16 No.4

Harmonics generated by the nonlinear loads and unbalancing of loads are serious concerns regarding the power quality of the distribution system. An Enhanced technique to scale down current harmonics, balance loads by MSALC (Modifi ed Shunt Active Line Conditioner) using traditional PI and enhanced FoPID (Fractional order PID) control device is presented in the article. Performance of MSALC using traditional PI and enhanced FoPID is tested for various load conditions and dynamic load changing characteristics were performed. Using MATLAB/Sim software the outcomes are verifi ed. Comparatively harmonic current reduction between traditional PI and enhanced FoPID was discussed. Enhanced FoPID control device-based MSALC found to have superior performance than the traditional PI-based MSALC.

고속철도 전철변전소 피크전력 저감을 위한 기술개발 연구

임성수(Sung-Soo Lim),편장식(Jang-Sik Pyun),권경민(Kyoung-Min Kwon) 한국철도학회 2015 한국철도학회 학술발표대회논문집 Vol.2015 No.10

고속열차는 대용량 부하로서 열차 운행을 위한 필요한 전력을 각 구간에 설치된 고속철도 전철변전소에서 공급받고 있으나 운영환경 변화에 따라 고속철도 변전소의 피크전력이 점진적으로 증가하고 있는 추세이다. 피크전력의 증가는 변전소의 설비비용 증가 및 전력사용요금을 증가시키는 요인이 되고 있다. 또한 고속철도 등 전기철도에서는 견인전동기 구동으로 인해 부하의 변동이 심하고 고조파가 발생하여 통신유도장애, 과전류, 계전기, 변압기 오동작 및 소손 등과 같은 악영향을 미치게 된다. 이에 본 연구에서는 고조파 및 피크전력 관리를 목적으로 개발되고 있는 피크전력 저감장치와 능동형 고조파 필터에 대해 소개하고자 한다. These high-speed railways is increased the peak power due to load fluctuation occurrence in accordance with the operating status of the train, and it causes the energy costs increase. In addition, harmonic generated from the traction motor of high-speed railways, and it will have adverse effects such as communication induction failure of power equipment, over-current and malfunction. In this study, we introduce a research development results of active harmonic filter and peak power reduction device that has been developed for harmonic management and peak power reduction.

Bio-structural monitoring of bone mineral alterations through electromechanical impedance measurements of a Piezo-device joined to a tooth

Tinoco Hector A.,Cardona Carlos I.,Marín-Berrio Maribel L. F.,García-Grisales Juliana,Gomez Juan P.,Roldan Samuel I.,Peña Fabio M.,Brinek Adam,Kalasová Dominika,Kaiser Jozef,Zikmund Tomas 대한의용생체공학회 2020 Biomedical Engineering Letters (BMEL) Vol.10 No.4

Bone presents different systemic functionalities as calcium phosphate reservoir, organ protection, among others. For that reason, the bone health conditions are essential to keep in equilibrium the metabolism of several body systems. Different technologies exist to diagnose bone conditions with invasive methods based on ionizing radiation. Therefore, there is a challenge to develop new ways to evaluate bone alterations in a noninvasive form. This study shows the assessment of a piezo-actuated device acting on a human tooth for the bio-monitoring of bone alterations. The bone diagnosis is performed by applying the electromechanical impedance technique (EMI), commonly used in structural health monitoring. For the experimental tests, five bone samples were prepared, and one was chosen as the monitoring. All samples were put in a decalcifying substance (TBD1 acid–base) at different times to emulate localized bone mineral alterations. Bone reductions were computed by using X-ray micro-computed tomography analyzing the morphometry. Electrical resistance measurements (piezo-device) were taken for the monitoring specimen meanwhile it was partially decalcified during 8520 seconds. In the frequency spectrum, several observation windows showed that the bone alterations gradually changed the electrical resistance signals which were quantified statistically. Results evidenced that the bone density changes are correlated with the electrical resistance measurements; these changes presented an exponential behavior as much as in the calculated index, and bone mineral reduction. The results demonstrated that bone alterations exhibit linear dependence with the computed statistical indexes. This result confirms that it is possible to observe the bone changes from the teeth as a future application.