• Structural Engineering and Mechanics
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• 제28권4호
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• pp.387-410
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• 2008

The fatigue damage accumulation rates of horizontally curved thin walled box-girder bridge have been estimated from vehicle-induced dynamic stress history using rain flow cycle counting method in the time domain approach. The curved box-girder bridge has been numerically modeled using computationally efficient thin walled box-beam finite elements, which take into account the important structural actions like torsional warping, distortion and distortional warping in addition to the conventional displacement and rotational degrees of freedom. Vehicle model includes heave-pitch-roll degrees of freedom with longitudinal and transverse input to the wheels. The bridge deck unevenness, which is taken as inputs to the vehicle wheels, has been assumed to be a realization of homogeneous random process specified by a power spectral density (PSD) function. The linear damage accumulation theory has been applied to calculate fatigue life. The fatigue life estimated by cycle counting method in time domain has been compared with those found by estimating the PSD of response in frequency domain. The frequency domain method uses an analytical expression involving spectral moment characteristics of stress process. The effects of some of the important parameters on fatigue life of the curved box bridge have been studied.

• Journal of Biosystems Engineering
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• 제33권1호
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• pp.38-44
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• 2008

The freight vehicle is mostly used to transport the fruit. Shock and impact generated by the freight vehicle may give serious damage to fruits hence to reduce the fruits damage, the optimum packaging design during transportation by vehicle is required. In order to design the packaging system for fruit transportation optimally, the comprehension of characteristic for vibration and shock acting on vehicles under various road conditions and loading methods is required. This research was performed to analyze the shock characteristics, acceleration level and power spectral density (PSD) of the fruit transportation vehicles under several travel roads and positions. The vibration signal was measured and analyzed at the transportation vehicle operating on the road of three different surface conditions. The maximum acceleration was measured at the rear-end of the vehicle, and the acceleration in the direction of up-and-down (z-axis) was much greater than those in the directions of back-and-forth (x-axis) or right-and-left (y-axis). The peak acceleration in the direction of up-and-down (z-axis) at the vehicle driving on the expressway, the local road paved with concrete, and unpaved local road were 5.3621 G, 8.232 G, and 14.162 G respectively. PSD at 2.44 Hz showed maximum value at all road conditions. The maximum values of PSD on the expressway, a local road paved with concrete, and unpaved local road were 0.0075222 $G^2/Hz$, 0.058655 $G^2/Hz$, and 0.24598 $G^2/Hz$ respectively. The value of PSD decreased with an increase of the vibration frequency of the transportation vehicle. In most cases, the vibration frequency was below 20 Hz during transportation.

• 한국전기전자재료학회논문지
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• 제21권8호
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• pp.770-775
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• 2008

Autonomic nervous system of the anesthetized patients can be influenced by the many kinds of stimulations such as intubation, surgical incision and so on. The changes of the heart rates and blood pressures are surrogates of responses of the autonomic system to the external stimulations. Recently, the power spectral analysis of the heart rate variability (HRV) made it easy to know the fractions and changes of sympathetic and parasympathetic autonomic systems. In this study, the changes of pulse transit time, one of the response of vessels to stimulations, was investigated in relation to the HRV. Ten patients were examined and average age is 22.5 $\pm$ 11.04, average weight is 63 $\pm$ 14.4 kg. The patients were anesthetized only by sevoflurane inhalation. Pulse transit time is determined by calculating the difference of the time between the R peak of ECG and the characteristic point of the plethysmography. Power spectral density (PSD) of the HRV was achieved in the frequency of 0.04-0.15 (LF) and 0.15-0.4 (HF). Compared to preanesthetic period the values of LF and LF/HF ratio of HRV were decreased (p<0.05). HF and PTT was increased in anesthetic state with sevoflurane. Otherwise, after intubation, the HF was decreased and LF, LF/HF ratio and PTT were increased. PSD of the HRV is well-known for the index of the autonomic nervous activity. Not only HRV but PTT analysis also is a useful index reflecting the autonomic responses to various stimulations. And this analysis is useful in bed side monitoring because the calculating method is simple and it takes shorter processing time compared to the HRV analysis.

• 한국전자파학회논문지
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• 제9권3호
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• pp.347-358
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• 1998

복잡하고 다양한 전파 환경을 라이시안 채널로 모델링할 수 있는 가능성에 대해서 검토해 보았다. 라이시안 채널에서의 수신 신호를 컴퓨터 시뮬레이터를 제작하여 모의 실험하였고, 모의 실험된 신호의 PDF(포락선 크기의 분포), PSD(Power Spectral Density), LCR(Level Crossing Rate), ADF(Average Duration of Fades), BER(Bit Error Rate)를 이론치와 비교한 결과 매우 잘 일치함을 확인할 수 있었다.

• Corrosion Science and Technology
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• 제2권1호
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• pp.18-25
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• 2003

Effects of the precipitation of $\sigma$ phase on the metastable pitting as a precursor of stable pitting corrosion and also on the progress of stale pitting of the 25Cr-7Ni-3Mo-0.25N duplex stainless steel were investigated in chloride solution. Electrochemical potential and current noises of the alloy were measured in 10 % ferric chloride solution ($FeCl_3$) with zero resistance ammeter (ZRA), and then analyzed by power spectral density (PSD) and by corrosion admittance ($A_c$) spectrum. With aging at $850^{\circ}C$, the passive film of the alloy was found to get significantly unstable as represented by power spectral density (PSD) and a transition from metastable pitting state to stable one was observed. In the corrosion admittance spectrum, the number of negative $A_c$ corresponding to the state of localized corrosion increased with aging, suggesting that the precipitation of $\sigma$ phase considerably degraded the passive film by depleting Cr and Mo around it at $\alpha/\sigma$ or $\gamma/\sigma$ phase boundaries, thereby leading to the initiation of the pitting corrosion. However, the Cr and Mo at $\alpha/\sigma$ or $\gamma/\sigma$ phase boundaries which were once depleted due to the precipitation of the $\sigma$ phase were partly replenished by the diffusion of Cr and Mo from the surrounding matrix with aging time longer. The initiation of pitting seems to be associated with the precipitation density of the $\sigma$ phase with an effective size needed to induce the sufficient depletion of Cr and Mo around it.

• 한국전기전자재료학회논문지
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• 제22권6호
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• pp.537-545
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• 2009

In this paper, new parameters were developed to estimate the depth of anesthesia during a general anesthesia using EEG. Power spectral density(PSD) analysis was used for these parameters because EEG became slow wave during anesthesia. The new parameters were DTR, ATR, TDR, ADR, BTR and BDR applied to PSD. These parameters were compared with SEF which is conventionally used at clinic and confirmed clinical value. As the results, DTR, ATR, TDR, ADR among parameters were not useful compared with SEF but BTR and BDR is valuable for clinic. 15 patents, at pre-operation BDR the value is $265.36{\pm}25.29$, at induction the value is $129.23{\pm}34.92$, at operation the value is $154.99{\pm}38.34$, at awaked the value is $283.83{\pm}39.80$ and at post-operation the value is $234.80{\pm}23.46$. Also at pre-operation BTR value is $183.38{\pm}13.59$, at induction the value is $104.09{\pm}25.11$, at operation the value is $115.38{\pm}23.42$, at awaked the value is $190.33{\pm}23.31$ and at post-operation the value is $172.38{\pm}19.08$. Trend of BDR and BTR is similar to change of SEF, so two parameters are useful. to estimate the depth of anesthesia.

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

• 한국기계가공학회지
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• 제21권6호
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• pp.67-73
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• 2022

Industrial inverters are used in a variety of fields for electric power supply. They may be exposed to vibration and heat once they are installed. This study focused on a framework of accelerated life testing of an industrial inverter considering fatigue damage as the primary source of deterioration. Instead of analyzing detailed failure mechanisms and the product's vulnerability to them, the potential of fatigue failure is considered using the fatigue damage spectrum calculated from the environmental vibration signals. The acceleration and temperature data were gathered using field measurement and spectral analysis was conducted to calculate the vibration signal's power spectral density (PSD). The fatigue damage spectrum is then calculated from the input PSD data and is used to design an accelerated fatigue life testing. The PSD for the shaker table test is derived that has the equivalent fatigue damage to the original input signal. The tests were performed considering the combined effect of random vibration and elevated temperature, and the product passed all the planned tests. It was successfully demonstrated that the inverter used in this study could survive environmental vibration up to its guarantee period. The fatigue damage spectrum can effectively be used to design accelerated fatigue life testing.

• 에너지공학
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• 제29권3호
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• pp.7-17
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• 2020

배열회수보일러는 가스터빈의 고온의 배기가스 에너지를 이용하여 증기를 발생시키는데 고속의 배기 가스에 의해 유체유발진동이 발생하여 다수의 구조물 파손이 발생한다. 구조물의 파손을 예측하기 위한 피로수명 평가는 유체유발 진동으로 발생하는 진동분석을 통해 PSD(Power Spectral Density)을 도출해야 하지만, 가스터빈의 배기가스 유동 형태가 매우 빠르고 복잡하여 발생되는 진동을 이론, 실험적으로 도출되는 것은 매우 어렵다. 하지만 LES(Large Eddy Simulation) 적용을 통해 구조물의 위치에 따라 진동 특성을 파악할 수 있는 방법을 정립하였고, 이러한 진동 특성을 구조 해석에 적용하면 구조물 피로수명 평가에 활용할 수 있다.

• 한국운동역학회지
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• 제25권3호
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• pp.283-291
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• 2015

Objective : The purpose of this study was to determine the differences in the head and tibial acceleration signal magnitudes, and their powers and shock attenuations between flat-footed and normal-footed running. Methods : Ten flat-footed and ten normal-footed subjects ran barefoot on a treadmill with a force plate at 3.22m/s averaged from their preferred running speed using heel-toe running pattern while the head and tibial acceleration in the vertical axis data was collected. The accelerometers were sampled at 2000 Hz and voltage was set at 100 mv, respectively. The peak magnitudes of the head and tibial acceleration signals in time domain were calculated. The power spectral density(PSD) of each signal in the frequency domain was also calculated. In addition to that, shock attenuation was calculated by a transfer function of the head PSD relative to the tibia PSD. A one-way analysis of variance was used to determine the difference in time and frequency domain acceleration variables between the flat-footed and normal-footed groups running. Results : Peaks of the head and tibial acceleration signals were significantly greater during flat-footed group running than normal-footed group running(p<.05). PSDs of the tibial acceleration signal in the lower and higher frequency range were significantly greater during flat-footed running(p<.05), but PSDs of the head acceleration signal were not statistically different between the two groups. Flat-footed group running resulted in significantly greater shock attenuation for the higher frequency ranges compared with normal-footed group running(p<.05). Conclusion : The difference in impact shock magnitude and frequency content between flat-footed and normal-footed group during running suggested that the body had different ability to control impact shock from acceleration. It might be conjectured that flat-footed running was more vulnerable to potential injury than normal-footed running from an impact shock point of view.