• Structural Engineering and Mechanics
• /
• 제71권3호
• /
• pp.291-303
• /
• 2019

In the paper the analysis of natural vibrations of the transmission line with use of spectral elements and the laboratory experiments is performed. The purpose of the investigation is to analyze the natural vibrations of the transmission line and compare with the results obtained in the numerical simulations. Particular attention is paid to the hysteretic and aerodynamic damping analysis. Sensitivity of the wave number is performed for changing of the tension force, as well as for the different damping parameters. The numerical model is made using the Spectral Element Method. In the spectral model, for various parameters of stiffness, damping and tension force, the system response is checked and compared with the results of the accelerations obtained in the measurements. A frequency response functions (FRF) are calculated. The credibility of the model is assessed through a validation process carried out by comparing graphical plots of FRF and time history analysis and numerical values expressing differences in acceleration amplitude (MSG), phase angle differences (PSG) and differences in acceleration and phase angle total (CSG) values. The next aspect constituting the purpose of this paper is to present the wide possibilities of modelling and simulation of slender conductors using the Spectral Element Method. The obtained results show good accuracy in the range of both experimental measurements as well as simulation analysis. The paper emphasizes the ease with which the sensitivity of the conductor and its response to changes in density of spectral mesh division, tensile strength or material damping can be studied.

• 자원환경지질
• /
• 제36권3호
• /
• pp.201-212
• /
• 2003

한반도 남동부의 경상분지에 한국지질자원연구원의 지진관측망을 비롯한 관측소들이 급격히 증가함에 따라, 지진관측의 능력이 최근에 들어 크게 향상되었다. 그러나, 빈번한 중소규모의 화약발파에 의한 진동이 다수 관측되고 있다. 따라서, 이 지역에서 자연지진과 발파에 의한 인공지진의 식별이 중요한 문제로 부상하였다. 이 지역에서의 인공지진과 자연지진의 적절한 식별법을 확립하기 위하여 소규모의 지역지진 43개와 이에 대응되는 인공지진 43개를 선정하였다. 이 연구에서는 주파수 영역에서 Pg파, Sg파 및 Lg파의 스펙트럼 진폭비를 이용하는 기법들이 폭 넓게 검토되었다. 그들 중 Pg/Lg 스펙트럼 진폭비를 이용하는 방법이 가장 좋은 식별법으로 나타났다. 또한, 식별능력을 향상시키기 위하여 Pg/Lg 스펙트럼비에 다변량 판별분석법을 적용하였다. 거리보정이 안된 수직성분에 비하여 거리에 대한 감쇠효과를 보정한 3성분의 Pg/Lg비에 판별분석법을 적용했을 때의 판별능력은 뚜렷한 증가를 보인다. 주파수 대역 4-l4Hz의 범위에서, 거리 보정한 3성분의 Pg/Lg비에 대한 판별분석의 결과 총 분류비율은 0.89%에 불과한 것으로 나타난다.

• The Journal of Advanced Prosthodontics
• /
• 제8권3호
• /
• pp.187-193
• /
• 2016

PURPOSE. This pilot study was to find the influence of complete denture on the brain activity and cognitive function of edentulous patients measured through Electroencephalogram (EEG) signals. MATERIALS AND METHODS. The study recruited 20 patients aged from 50 to 60 years requiring complete dentures with inclusion and exclusion criteria. The brain function and cognitive function were analyzed with a mental state questionnaire and a 15-minute analysis of power spectral density of EEG alpha waves. The analysis included edentulous phase and post denture insertion adaptive phase, each done before and after chewing. The results obtained were statistically evaluated. RESULTS. Power Spectral Density (PSD) values increased from edentulous phase to post denture insertion adaption phase. The data were grouped as edentulous phase before chewing (EEG p1-0.0064), edentulous phase after chewing (EEG p2-0.0073), post denture insertion adaptive phase before chewing (EEG p3-0.0077), and post denture insertion adaptive phase after chewing (EEG p4-0.0096). The acquired values were statistically analyzed using paired t-test, which showed statistically significant results (P<.05). CONCLUSION. This pilot study showed functional improvement in brain function of edentulous patients with complete dentures rehabilitation.

• 조명전기설비학회논문지
• /
• 제27권12호
• /
• pp.63-73
• /
• 2013

The parameters of electromechanical modes offer considerable insight into the dynamic stability properties of a power system. This paper presents a results of a LFO(low-frequency oscillation) based on the time-synchronized signals measured by synchrophasor in the rolling blackout. Spectral analysis was performed, and critical parameters were estimated using the data acquired from synchrophasors installed in the KEPCO system. As significant modes, a 0.68 Hz oscillation mode that occurred prior to the forced load shedding in the rolling blackout was estimated. Such an oscillation mode can cause an uncontrollable blackout. Therefore, the system should be operated so that significant oscillation modes are not activated. This results can serve as a reference in the future for reliable system operation in the event of a similar blackout.

• 대한토목학회논문집
• /
• 제28권1A호
• /
• pp.59-67
• /
• 2008

원전 구조물의 내진해석에서 사용하는 시간이력 함수는 적절한 하중을 보장하기 위하여 설계응답스펙트럼에 부합할 뿐만 아니라 최소 PSD함수 이상의 PSD함수를 갖도록 함으로서 각각의 진동수에서 일정 크기 이상의 에너지를 갖고 있어야 한다. 도로교 구조물에서도 구조물의 대형화와 정교화로 인한 구조물의 공공 기능의 안전성이 더욱 강조되어, 설계 목적의 PSD함수의 규정이 필요하지만 적절한 절차가 개발이 되지 않아 현실적으로 적용하기 어려운 실정이다. 본 연구에서는 다수의 인공지진을 이용하여 표준 PSD함수를 계산하는 절차를 제시하고 현재의 도로교 내진설계 스펙트럼에 부합하는 표준 PSD 함수를 제안하였다.

• Journal of Oral Medicine and Pain
• /
• 제22권1호
• /
• pp.145-155
• /
• 1997

The purpose of this study was to compare differences in endurance time and EMG power spectral characteristics of the masticatory muscles during sustained isometric contraction between patients and controls. 15 CMD patients{8 women and 7 men, aged 15 to 38 years(24.1$\pm$7.5)}, and 15 healthy volunteers{8 women and 7 men, aged 15 to 30 years(24.7$\pm$3.4)} without past history or present symptoms of CMD were included in this study. Sustained isometric contractions of masticatory muscles were perfomeed as long as possible at 50% level of maximum voluntary contraction(MVC) of EMG activity via visual feedback, and the duration of sustained isometric contraction(endurance time) was examined. The author perfomed EMG power spectral analysis in the myoelectric signals of masseter and anterior temporal muscle during sustained isometric contraction in CMD patients with chronic muscle pain and healthy controls. The author came to following conclusions from the results. 1. The endurance time of the patient group was shorter than the control group in sustained isometric contraction of masticatory muscles(p<0.01). 2. MF values of masticatory muscles with sustained isometric contraction during endurance time were decreased following regression line in both groups(p<0.01, r>0.9). 3. The amount of MF shift to lower frequency range exhibited no significant differences between the patients and the control group in sustained isometric contraction during endurance time. 4. SMF to lower frequency range of the patient group was steeper than the control group in sustained isometric contraction during endurance time(p<0.05).

• 대한화학회지
• /
• 제29권4호
• /
• pp.382-389
• /
• 1985

Inductively coupled plasma(ICP)법을 이용하여 희토류원소들을 정량분석할 때 플라스마 작동 조건이 미치는 영향에 관하여 연구하였다. 플라스마 작동시 시료운반기체의 사용량을 증가시키면 희토류원소 스펙트럼선들의 검출한계는 낮아지나 이온화 방해 영향이 증가되었다. RF power의 변화는 이온화 방해에는 큰 영향을 미치지 않지만 바탕세기에 대한 스펙트럼선 세기의 비율은 RF power가 감소될수록 증가되었다. 플라스마내에서 이온화 방해 영향이 작은 위치는 스펙트럼선의 spacial profile이 최대가 되는 부분보다 약간 높은 위치이었다. 희토류원소의 분석시 많이 이용되는 스펙트럼선들의 검출한계를 측정하고 비교적 간섭영향이 작은 스펙트럼선을 선정하였다.

• Earthquakes and Structures
• /
• 제13권2호
• /
• pp.193-200
• /
• 2017

To overcome the difficulty of performing multi-point response spectrum analysis for engineering structures under spatially varying ground motions (SVGM) using the general finite element code such as ANSYS, an approach has been developed by improving the modelling of the input ground motions in the spectral analysis. Based on the stochastic vibration analyses, the cross-power spectral density (c-PSD) matrix is adopted to model the stationary SVGM. The design response spectra are converted into the corresponding PSD model with appropriate coherency functions and apparent wave velocities. Then elements of c-PSD matrix are summarized in the row and the PSD matrix is transformed into the response spectra for a general spectral analysis. A long-span high-pier bridge under multiple support excitations is analyzed using the proposed approach considering the incoherence, wave-passage and site-response effects. The proposed approach is deemed to be an efficient numerical method that can be used for seismic analysis of large engineering structures under SVGM.

• 비파괴검사학회지
• /
• 제19권2호
• /
• pp.85-92
• /
• 1999

비선형 음향효과를 계측함에 의해서 재료열화를 평가하는 연구는 오래 전부터 있어 왔다. 여기서, 비선형 음향효과를 계측하는 가장 일반적인 방법은 전파된 수신 신호에서 기본주파수 성분과 2차 고조파 성분의 절대적인 크기를 계측하는 것이다. 이 목적을 위해서 일반적으로 파워스펙트럼 해석법이 널리 사용되어 왔다. 그러나, 파워스펙트럼은 신호처리 후에도 주파수 영역에서 가우스 잡음이 혼재한다는 단점이 있다. 게다가, 비선형 효과에 의해서 발생되는 2차 고조파 성분의 크기는 너무 작아서 잡음에 묻혀버릴 수도 있다. 본 논문에서는, 이 문제를 해결하기 위해서 주파수 영역에서 가우스 잡음을 제거할 수 있는 바이스펙트럼 해석법을 제안하였다. 시뮬레이션을 통하여 잡음이 크게 혼재된 신호에서도 참 값에 가까운 비선형 파라미터를 구할 수 있음을 밝혔다. 또한, 실제 경우에 이 방법의 유용함을 확인하기 위하여 피로 하중에 의해서 고의로 열화시킨 여러 시편에 대하여 파워스펙트럼과 바이스펙트럼을 구하여 비교하였다.

• 자원환경지질
• /
• 제31권1호
• /
• pp.53-57
• /
• 1998

Transient electromagnetic (TEM) method is also affected by cultural and natural electromagnetic (EM) noises, since it uses part of the broadband ($10^{-2}$ to $10^5Hz$) spectrum. Especially, predominant EM noise which affects a moving transmitter-receiver TEM system is sensor motion-induced noise. This noise is caused by the sensor motion in the earth magnetic field. The technique for reducing the sensor motion-induced EM noise presented in this paper is based on Halverson stacking. This Halverson stacking is generally used in a time-domain induced polarisation (IP) system to reject DC offset and linear drift. According to spectrum analysis of the vertical component of sensor motion-induced noise, the frequency range affected by the motion of an EM sensor is less than about 700 Hz in this study. With the decrease of the frequency, the spectral power caused by the motion of a sensor increases. For example, at the frequency of 200 Hz, the spectral power of the sensor motion-induced noise is $-90dBVrms^2$ while the spectral power of the EM noise measured with a fixed sensor on the ground is $-105dBVrms^2$, and at the frequency of 100 Hz, the spectral power of the sensor motion-induced noise is $-70dBVrms^2$ while the spectral power of the EM noise measured with a fixed sensor on the ground is $-105dBVrms^2$. With applying Halverson stacking to an artificial noise transient generated by adding a noise-free transient to sensor motion-induced noise measured without pulsing, it is shown that the filtered transient is nearly consistent with the noise-free transient within a delay time of $0.5{{\mu}sec}$. The inversion obtained from this filtered transient is in accord with the true model with an error of 5%.