• Title/Summary/Keyword: wave pressure function

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Plasma Assisted Nitriding of Stainless Steel Type 304L (304L 스테인리스 강의 플라즈마 질화처리)

  • Park, J.R.
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.4
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    • pp.255-265
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    • 1995
  • Stainless steel type 304L has been nitrided in the low pressure (600Pa) and high nitrogen (80% $N_2$+20% $H_2$) environment for 5 hours by the square-wave-pulsed-d.c. plasma as a function of temperature $400{\sim}550^{\circ}C$ and pulsation. At the lower temperature range of $400{\sim}500^{\circ}C$ and at the relatively high ratio of pulse duration to pulse period. "S-phase" has been developed in the form of thin nitrided surface layer which has many cracks, leading to be nearly impossible for the industrial anti-wear and anti-corrosion applications. At the higher temperature up to $550^{\circ}C$ with the increasing ratio of the pulse duration to pulse period up to $50{\mu}s/100{\mu}s$, the nitrided layer, whose growth rate has increased also, has been composed mainly of CrN and $Fe_4N$ phases and has become thick, uniform and nearly crack-free.

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Note on the Two-Microphone Methods for the Measurement of Acoustic Impedance (음향 임피던스 측정을 위한 이중 마이크로폰 기법에 대한 고찰)

  • SEO, SEONGHYEON
    • Journal of Hydrogen and New Energy
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    • v.29 no.2
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    • pp.163-169
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    • 2018
  • The present article discusses about the measurement techniques of acoustic impedance that becomes one of the important acoustic characteristics of various boundaries found inside of propulsion systems. Acoustic characteristics including acoustic impedance and reflection coefficient can be often assessed and estimated by use of the two-microphone method. Theoretical expressions of acoustic impedance and reflection coefficient measured in an impedance tube are presented for both cases with mean flow and without flow, and the practical application of the method through calibration is also provided. The acoustic impedance and the reflection coefficient are related with axial locations of microphones, thermodynamic characteristics of gas inside, and the transfer function between the pressure wave measurements at multiple locations.

Calculation of Unbalanced Magnetic Pull of Induction Motors due to Rotor Misalignment (경사 편심에 의한 유도전동기의 자기흡인력 평가)

  • Kim, S.H.;Yang, B.S.;Kim, H.C.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.05a
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    • pp.1321-1327
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    • 2006
  • This paper presents the calculation of unbalanced magnetic pull (UMP) that causes rotor misalignment in induction motor. The excessive noise and vibration will be occurred by means of rotor misalignment. Angular misalignment of rotor will produce air-gap permeance wave which is function of axial and circumferential coordinate. In this paper, the UMP is calculated using permeance and magneto motive force (MMF) in the case of static and dynamic misalignment. Based on the percentage of misalignment, the result shows that the UMP and magnetic pressure are increased according to the increasing of misalignment. The UMP is occurred not only in It frequency component but also the others.

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A Study on the Optimal Magnet for ECR (ECR 용 최적 마그네트에 관한 연구)

  • Kim, Y.T.;Kim, Y.J.;Kim, K.S.;Lee, Y.J.;Son, M.H.
    • Proceedings of the KIEE Conference
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    • 1992.07b
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    • pp.649-652
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    • 1992
  • ECR(Electron Cyclotron Resonance) occure at ${\omega}_c$=${\omega}$, ${\omega}_c$:electron cycltron frequency, ${\omega}$:electromagnetic wave frequency. ECR system have several merit, 1) power transefer efficiency 2) low neutral gas pressure (below 1 mTorr) 3) high plasma density($10^{12}$ $cm^{-3}$). It is applicated variously in the field of semiconductor and new materials as the manufacturing equipment. Magnetic field in ECR system contruct resonance layer (${\omega}$=2.45GHz, $B_z$=875 Gauss) and control plasma. Plasma is almost generated at resonance layer. If the distance between substrate and resonance layer is short, uniformity of plasma is related with profile of resonance layer. Plasma have the property "Cold in Field", so directonality of magnetic field is one of the control factors of anisotropic etching. In this study, we calculate B field and flux line distribution, optimize geometry and submagnet current and improve of magnetic field directionality (99.9%) near substrate. For the purpose of calculation, vector potential A(r,z) and magnetic field B(r,z), green function and numerical integration is used. Object function for submagnet optimization is magnetic field directionality on the substrate and Powell method is used as optimization skim.

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Comparison of the Effect of Ischemic Compression Therapy and Extracorporeal Shock Wave Therapy on the Trigger Point of the Upper Trapezius Muscle (위등세모근의 발통점에 대한 허혈성 압박치료와 체외충격파치료의 효과비교)

  • Joo, Ji-Kyun;Park, Sam-Ho;Shin, Won-Seob
    • Journal of The Korean Society of Integrative Medicine
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    • v.9 no.2
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    • pp.141-152
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    • 2021
  • Purpose: This study aimed to compare the effects of ischemic compression (IC) therapy and extracorporeal shock wave therapy (ESWT) in patients with upper trapezius myofascial pain syndrome and to present an effective treatment method for these patients. Methods: A total of 42 patients with upper trapezius myofascial pain syndrome were randomly assigned to the IC group (n = 21) and ESWT group (n = 21). IC therapy and ESWT were performed in the IC and ESWT groups, respectively. Treatment was applied to the trigger point of the upper trapezius muscle. Visual analog scales (VAS), pain pressure threshold (PPT), range of motion, neck disability index (NDI), and fear-avoidance belief questionnaire (FABQ) were evaluated before and after the intervention to compare its effectiveness. Results: Both groups showed significant differences before and after the intervention in VAS, PPT, NDI, FABQ, flexion, extension, right side bending, and left side bending (p <.05). In addition, there were significant differences in the IC group compared to the ESWT group in VAS, PPT, and NDI (p <.05). Conclusion: IC therapy and ESWT applied to patients with upper trapezius myofascial pain syndrome are mediating methods of pain, function, and psychosocial effects. In addition, IC therapy may be a more effective mediating method for pain and dysfunction than ESWT.

Combustion Experiments of a High Pressure Liquid Propellant Thrust Chamber (고압 실물형 연소기의 저압 및 설계점 연소시험)

  • Seo Seonghyeon;Han Yeoung-Min;Moon Il-Yoon;Lee Kwang-Jin;Song Joo-Young;Choi Hwan-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • v.y2005m4
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    • pp.269-273
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    • 2005
  • A practical, 30-tonf-class fullscale thrust chamber has been combustion tested using real propellants for the first time in the domestic technology scene. The very first combustion test was conducted at a low mass flow rate condition for the preliminary assessment of any problems associated with its function and performance while reducing risks from a high chamber pressure never achieved before. A test for the design condition achieved through a low-pressure stage shows stable characteristics of all the static pressures and thrust. Dynamic pressures measured in the manifolds and the chamber did not reveal any distinct wave coupled to a specific frequency and their intensities reside in the allowable range. Moreover, it is encouraging to find no physical failures with a thrust chamber hardware.

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Therapeutic Change of Sleep Structure and Function by Continuous Positive Airway Pressure Application in Obstructive Sleep Apnea Syndrome (폐쇄성(閉鎖性) 수면(睡眠) 무호흡증(無呼吸症)에서 지속적(持續的) 상기도(上氣道) 양압술(陽壓術)에 따른 수면구조(睡眠構造) 및 기능(機能) 변화(變化))

  • Jeong, Do-Un;Yoon, In-Young;Shim, Young-Soo
    • Sleep Medicine and Psychophysiology
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    • v.1 no.2
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    • pp.172-181
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    • 1994
  • Obstructive sleep apnea syndrome(OSAS) is most frequently diagnosed in the sleep laboratories and its severity is objectively estimated. In terms of treatment, the most prevalent method is the continuous positive airway pressure(CPAP) application as of now. However, in Korea, CPAP is still not sufficiently known and it is attributable to the fact that sleep study facilities have not been popularized. In this article, the authors present their own experience with CPAP in nine subjects with OSAS. In this study, CPAP was found to decrease stage 1 sleep and to increase stage 2 sleep, with increasing mean oxygen saturation and decreasing lowest oxygen saturation during nocturnal sleep. Also, it tended to increase sleep continuity and generally to improve sleep architecture. Rebound slow wave and/or REM sleep stages during CPAP were also noted in 8 out of 9 cases. The authors suggest that CPAP should be considered as the primary mode of treatment for patients with obstructive sleep apnea syndrome and related educational programs for physicians should be developed and provided by sleep specialists.

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Effect of Airborne Noise from Ship Machinery on Underwater Noise (선박의 장비 공기소음이 수중소음에 미치는 영향)

  • Kim, Hyun-Sil;Kim, Jae-Seung;Kim, Bong-Ki;Kim, Sang-Ryul;Lee, Seong-Hyun
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.6
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    • pp.569-574
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    • 2011
  • In research vessels or naval ships, airborne noise from machineries such as diesel engine is the major source of underwater noise at low speed. In this paper, effect of engine noise on underwater noise is studied by considering two paths; sound radiation from hull plate and direct airborne noise transmission through hull plate. SEA (Statistical energy analysis) is used to predict hull plate vibration induced by engine noise, where SEA model consists of only two subsystems; engine room air space and hull plate. The pressure level in water is calculated from sound radiation by plate. Engine noise transmission through hull plate is obtained by assuming plane wave propagation in air-limp plate-water system. Two effects are combined and compared to the measurement, where speaker is used as a source in engine room and sound pressure levels in engine room and water are measured. The hydrophone is located 1 m away from the hull plate. It is found below 1000 Hz, prediction overestimates underwater sound pressure level by 5 to 12 dB.

Development of Safe Stove System using Sound Wave Fire Extinguisher (음파 소화기를 이용한 안전 스토브 시스템 개발)

  • Seo, Yunwon;Lee, Sukjae;Park, yungjoo;Kim, Kinam;Choi, Yongrae;Hwang, Hyungjun;Han, Seunghan;Shim, Dongha
    • Fire Science and Engineering
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    • v.32 no.6
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    • pp.34-39
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    • 2018
  • In this paper, the architecture of a safe stove with an automatic fire suppression function using a sound wave fire extinguisher has been proposed and developed for the first time. A microcontroller connected to a fire sensor detects and suppresses a fire by driving a fire extinguisher. The sound wave fire extinguisher is composed of a speaker and collimator, and is driven by a driver module including an audio amplifier. The attenuation of the sound wave is reduced by preventing the sound diffusion with an enclosure surrounding a stove. The frequency of the sound wave is set to 50 Hz, and the sound pressure of 93 dBA is measured at the distance of 0.5 m. It takes maximum 8 and 15 seconds to suppress the flame from 7-cc and 14-cc flammable liquid, respectively, which corresponds to 24% and 42% of the natural extinguishing time. Since the proposed safe stove is non-toxic and leaves no residues over the conventional ones, it would combine with various home appliances to suppress early-stage fires and prevent fire expansion.

The Nonlinear Combustion Instability Prediction of Solid Rocket Motors (고체로켓모터의 비선형 연소 불안정성 예측 기법)

  • Hong, Ji-Seok;Moon, Hee-Jang;Sung, Hong-Gye;Um, Won-Seok;Seo, Seonghyeon;Lee, Do-hyung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.20 no.1
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    • pp.20-27
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    • 2016
  • The prediction of combustion instability is important to avoid an obvious threat to the structural safety and the motor performance because it affects the apparent response function of the propellant, the burning rate, and a mean flow Mach number at the local surface. The combustion instability occurs in case acoustic waves were coupled with the combustion/flow dynamic frequency. In this paper, an acoustic instability model is derived from the nonlinear wave equation for analysing acoustic dynamics in solid rocket motors. The chamber pressure and burning rate effects on combustion instability have been investigated.