• 한국정밀공학회지
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• 제12권11호
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• pp.132-139
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• 1995

Turbulent boundary layer pressure fluctuation exerted on the surface of a structure can give rise to a elastic stress wave on the surface of the structure. The stress wave so called surface wave, will not only propagate along the surface of structure but also penerate into the structure. To reduce the transmission of stress wave into the structure the elastomer layer is usually attactched on the surface of structure. The transfer function, which is defined herein as the ratio of stress waves at the surface and bottom of the elastomer layer, is derved by use of the cylindrical coordinates system. The elastodynamics of the elastomer layer subjected to the turbulent boundary layer pressure fluctuation is represented by the simplified one degree-of-freedom model for easy prediction of the stress wave transmission as well as efficient design of the elastomer layer.

• 감성과학
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• 제18권3호
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• pp.63-70
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• 2015

본 연구는 1/f fluctuation의 ${\alpha}$기울기 따라 구성된 사운드를 들었을 때 감정 스트레스 업무에 종사하고 있는 피험자들의 심박 변화를 확인하고자 하였다. 기존의 연구에서는 주로 사용자의 심리상태 안정시키는 효과 또는 생리적 안정성에 1/f fluctuation의 ${\alpha}$기울기가 관계가 있는 것으로 보고되었다. 본 연구에서는 1/f fluctuation 수준을 총 3가지 나누어 제작한 사운드를 독립변수로 사용하였다. 독립변수는 감정노동 종사자에게 제시하여 그에 따른 심장반응을 측정하였다. 종속변수는 네 가지로 BPM(Beat Per Minute), VLF(Very Low Frequency), SDNN(Standard Deviation of NN intervals), 그리고 HF(High Frequency) 파워(Power)값을 확인하였다. 분석결과 기울기가 3인 1/fluctuation 사운드는 각성효과를 보였다. 기울기 1, 2인 사운드는 이완효과가 있는 것을 통계적으로 검증하였다. 이러한 1/f fluctuation 사운드의 특성을 활용해 감정 노동자들의 스트레스를 완화시키기 위한 서비스에 응용될 수 있을 것으로 사료된다.

• 전기학회논문지
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• 제64권2호
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• pp.304-309
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• 2015

Applicable range of Photoplethysmography (PPG) becomes wider as a non-invasive physiological measurement technique. However, PPG waveform is easy to be distorted by ambient light or vascular variation from temperature changes. Especially, irregular variation of PPG waveform caused by ambient temperature not only severely distorts the PPG, but also leads miss interpretation in clinical applications. Therefore, the investigation of between temperature and PPG waveform is quite important in using PPG. The purpose of this research is to quantify the PPG waveform characteristic and to investigate the waveform variation following the temperature change on measuring site. To quantify the fluctuation of PPG waveform, we use two techniques; detrended fluctuation analysis (DFA) and AC/DC analysis of PPG. We record PPG under temperature stress, which applied by medical use heat pack ($40^{\circ}C$) and ice pack ($0^{\circ}C$). Ten participants were applied to the experiment, and the result was evaluated to approve the temperature effect with statistical method, Wilcoxon signed rank test. The result shows that the AC component (p<0.05) and perfusion index DFS scale exponent (p<0.01) of PPG have the significance to temperature stress except for a DC component of PPG.

• 오토저널
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• 제12권3호
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• pp.41-52
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• 1990

In this study are determined the unsteady temperature and thermal stress fields for a domestic 4-cylinder, 4-cycle gasoline engine cylinder head by the three-dimensional finite element method. A representative part of the cylinder head is modelled as a combination of hexahedron isoparametric elements, and the time-dependent temperature and the heat transfer coefficient of the gas are imposed as the thermal boundary conditions for the engine speeds of 500 rpm and 2000 rpm. The obtained results, which are represented graphically, indicate that the amplitudes of temperature fluctuation during a cycle are about 10.deg. C and 3.deg. C respectively on the surface of combustion chamber, and the maximum temperature fields occur at 30.deg. , 10.deg. respectively before the initiation of the exhaust stroke. Thermal stress fields due to non-uniform temperature distributions show that compressive stress is much larger than tensile stress throughout a cycle. It is also found that the compressive stress varies with substantial amplitude between the exhaust port and ignition plug hole, and the high tensile stress with small fluctuation occurs between exhaust port and the adjacent head bolt hole.

• 대한기계학회논문집
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• 제15권2호
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• pp.404-412
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• 1991

In the design of high speed machinery, designers must consider the problem of possible structural failure due to excessive dynamically varying stresses, which are induced by the varying external loads and internal inertia forces, in the links of the mechanism. A study of the dynamically induced stresses would indicate what values of the minimum permissible fatigue strength should be for safe mechanism operation. This paper investigates the nature of the stress fluctuation in high speed mechanism on the basis of the effects of both the loads and the friction. The latter is apt to be neglected in the usual analysis in spite of the fact that it is always generated in the operating machinery. The analysis is performed on the coupler of the slider-crank mechanism for illustrative purposes and the results are expressed in a non-dimensional form for design applications.

• 생태와환경
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• 제56권4호
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• pp.420-429
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• 2023

This study was designed to examine the immune response in Korean rockfish during water temperature fluctuation and to elucidate the factors contributing to streptococcal pathogenesis in cultured Korean rockfish, S. schlegeli. We investigated cumulative mortality against Streptococcus iniae (FP5228 strain) infection in the exposed Korean rockfish (39.7±5.8 g) to environmentally relevant temperature (Control, 23℃; High temperature, 28℃ and 23℃ and 28℃ with 12 hours interval exchange, 23↔28℃) for 48 hours. Also, the expression of the mRNA related to the immune response genes (heat shock protein 70, interleukin1β, lysozyme g-type and thioredoxin-like 1) were measured in spleen and head kidney by real-time PCR analysis in the exposed fish to thermal stress. In this study, the combined stress with bacterial challenge in fishes exposed to thermal stress lowered the survival rate than that of control (23℃). The cumulative mortality in the group of control, 28℃ and 23↔28℃ was 24%, 24% and 40% (P<0.05), respectively. Also, thermal stress modulated the mRNA level of immune related genes; heat shock protein 70, interleukin-1β, lysozyme g-type and thioredoxin-like 1 in Korean rockfish. The present study indicates that a high and sudden water temperature change affect immune responses and reduce the disease resistance in Korean rockfish.

• 수산해양기술연구
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• 제35권1호
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• pp.50-53
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• 1999

In this paper, the mechanical movement of lip seal-ring which plays the most important function in stern-tube sealing system and the possibility of leakage caused by pressure fluctuation are studied by theory and experiment. By the finite element method for axial symmetry object which receives the torsional bending load, the displacement and stress analysis of the seal-rings are executed for products of several representative manufacturers of seal-rings, and also the possibility of crack occurance are checked by theoretical analysis. A sample seal-ring id designed and manufactured using the program of displacement and stress analysis developed in this study and made an experimental apparatus to test the sampling seal-ring. The sampling seal-ring functioned excellently, but it had its durability and this problem may be solved by using the Viton instead of NBR.

• 한국지반공학회논문집
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• 제17권6호
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• pp.149-162
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• 2001

삼랑진에 위치한 삼랑진양수발전 상.하부댐의 댐마루에 시공 후 종방향 균열이 발생하였다. 이 댐들은 전력을 생산하기 위한 양수발전댐으로 상부댐과 하부댐으로 구성되어 있으며, 매일 10m이상의 수위변화를 받아왔다. 본 논문은 이들 댐중 상부댐에 발생한 종방향 균열의 원인을 찾는데 있다. 균열의 주요 원인은 수위변동으로 인한 것으로 판단되었으며, 이를 검토하기 위해 hyperbolic model을 이용한 수치해석을 수행하였다. 수치해석을 위한 입력자료를 얻기 위해 심벽재료와 사석재료에 대해 일련의 삼축압축시험을 수행하였다. 또한 수위변동으로 인한 주기적인 응력변화를 검토하기 위한 입력자료를 얻기 위해 진동삼축압축시험을 수행하였다. 수치해석결과 반복하중이 작용했을 경우 댐마루에서 깊이 4m까지 구속압력이 음이 되는 것으로 나타났으며, 이로 인해 종방향균열이 발생한 것으로 판단되었다. 이 종방향균열의 깊이는 댐 마루에서 수행한 시험굴에서 확인하였으며, 현장 조사결과와 잘 부합하였다.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권2호
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• pp.116-124
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• 2012

Wind is an abundant source of natural energy which can be utilized to generate power. Wind velocity does not remain constant, and as a result the output power of wind turbine generators (WTGs) fluctuates. To reduce the fluctuation, different approaches are already being proposed, such as energy storage devices, electric double layer capacitors, flywheels, and so on. These methods are effective but require a significant extra cost to installation and maintenance. This paper proposes to reduce output power fluctuation by controlling kinetic energy of a WTG system. A MW-class pitch-regulated permanent magnet synchronous generator (PMSG) is introduced to apply a power fluctuation reducing method. The major advantage of this proposed method is that, an additional energy storage system is not required to control the power fluctuation. Additionally, the proposed method can mitigate shaft stress of a WTG system. Which is reflected in an enhanced reliability of the wind turbine. Moreover, the proposed method can be changed to the maximum power point tracking (MPPT) control method by adjusting an averaging time. The proposed power smoothing control is compared with the MPPT control method and verified by using the MATLAB SIMULINK environment.

• 한국산학기술학회논문지
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• 제19권1호
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• pp.615-621
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• 2018

본 연구에서는 에너지절감과 실내쾌적성을 높이기 위하여 색온도, 아로마 및 소리 변동리듬의 자극을 가하여 비교분석하였다. 온도$25[^{\circ}C]$, 상대습도 50[RH%], 기류속도 0.02[m/s] 및 조도 1000[lux]가 유지되는 항온항습실에서 뇌파, 심박동 변이 및 바이브라이미지가 측정되었다. 자극 종류는 자극을 가하기 전, 소리 변동리듬 a=1.106 재즈 음원으로 이루어지는 단일자극 그리고 붉은 조명, 아로마향기 및 소리 변동리듬 a=1.106 재즈 음원으로 이루어지는 다감각자극의 세종류로 측정이 이루어졌다. 변동리듬 a=1.106의 재즈 음원, 붉은 조명 및 아로마향기의 다감각자극에서 생산성과 집중력이 향상되었고, 스트레스지수와 피로도가 감소되었다. 또한 변동리듬 a=1.106의 재즈음원, 붉은 조명 및 아로마향기의 다감각자극에서 심박동이 안정되게 유지되었으며, 바이브라이미지의 긴장도와 스트레스 역시 감소되었다. 변동리듬 a=1.106 음원, RED조명 및 쟈스민 향기의 다감각자극이 쾌적성과 집중력 향상에 효과적이라는 것을 알 수 있었으며, 단일감각에 노출되기 전보다 뉴로에너지가 증가한다는 것을 알 수 있었다. 변동리듬 a=1.106 음원, RED조명 및 쟈스민 향기의 다감각자극이 자극을 가하기전보다 또한 단일감각자극을 가했을 때 보다 뉴로에너지가 증가된다는 것을 알 수 있었다.