• 설비공학논문집
• /
• 제7권1호
• /
• pp.132-141
• /
• 1995

Characteristics of pressure-drop oscillations(PDO) in a boiling channel were studied numerically and compared with experimental data. Effects of initial and boundary conditions on PDO were investigated in terms of oscillation period and amplitude. The period and amplitude of PDO increased with increasing of the compressible volume in the surge tank and the heat input. PDO occurred within the specific range of the fluid temperature, at which oscillation period and amplitude diminished rapidly with the increase of the fluid temperature. The increase of the loss coefficient in fluid supply line resulted in slightly longer oscillation period and larger amplitude. Numerical results showed good agreement with the experimental data.

• Fisheries and Aquatic Sciences
• /
• 제16권3호
• /
• pp.211-220
• /
• 2013

A shaking motion could be used to improve fish escapement from a cod-end net by creating a sieving effect over the swept volume or by disturbing the optomotor response of the fish. In this study, a perpendicular shaking motion was generated in a towed cod-end net by a circular canvas attached to the end of the codend, which formed a biased cap-like shape. This concept was tested by using a model in a flow tank and by towing a prototype cod-end during sea trials. For the model tests, the amplitude of the shaking motion was $0.6{\pm}0.1$ times the rear diameter of the cod-end, and the period of the shaking motion was $2.6{\pm}0.1$ s at a flow velocity of 0.6 or 0.8 m/s. In the sea trials, the amplitude was $0.5{\pm}0.2$ times the rear diameter of the cod-end, and the period of the shaking motion was $7{\pm}4$ s at towing speeds of 1.2 or 1.7 m/s. Thus, the shaking amplitude during the sea trials was equal to or less than that observed in the tank tests, and the shaking period was twice as long. The shaking motion described by the amplitude and period could be an effective means to stimulate fish escapement from cod-end during fishing operations considering the response of the fish.

• 설비공학논문집
• /
• 제5권3호
• /
• pp.179-186
• /
• 1993

The characteristics of pressure-drop oscillations(PDO) in boiling channel are studied experimentally. The effects of initial and boundary conditions on PDO are investigated in terms of oscillation period and amplitude. The period and amplitude of PDO are increased with the increase in the compressible volume in surge tank and heat input. However the amplitude of PDO is decreased with fluid temperature under low subcooling condition. Higher initial insurge flowrate resulted in almost invariant oscillation period but lower amplitude. At higher heat input the oscillation of heater wall temperature is significant, whose period is the same as that of pressure-drop instability.

• Fisheries and Aquatic Sciences
• /
• 제16권2호
• /
• pp.101-108
• /
• 2013

An active stimulating device (ASD) consisting of a net panel or ropes fluttering in the turbulence inside the cod end was effective in driving fish near the cod end to reduce juvenile by-catch. The fluttering characteristics of the rope and net panel were examined by video observations and analyzed for fluttering amplitude and period in a water channel and in field experiments with a bottom trawl. The amplitude ratio of the fluttering ropes or nets in the tank test increased with the fluttering index as the diameter of the twine, mesh size, flexibility, and flow velocity changed, whereas the period decreased with the above factors. In bottom trawl experiments, the range of mean depth difference in the fluttering net panel was 12-17% of the length of the fluttering net, and the period of depth difference or three-dimensional (3D) tilt was revealed, with shorter ones ranging from 2 to 6 s. The amplitude as depth difference and period from field measurements were similar to those of nets in tank experiments and also to the period of 3D flow velocity inside the cod end. These results could be used to design an ASD that could be used for to the cod end of actual towed fishing gear to reduce juvenile by-catch.

• Earthquakes and Structures
• /
• 제20권4호
• /
• pp.457-471
• /
• 2021

This study aims at providing a simple and effective methodology to define a meaningful characteristic period for special class of earthquake records named "pulse-like ground motions". In the proposed method, continuous wavelet transform is employed to extract the large pulse of ground motions. Then, Fourier amplitude spectra obtained from the original ground motion and the residual motion is simply compared. This comparison permits to define a threshold pulse-period (Tp∗) as the threshold period above which the pulse component has negligible contributions to the Fourier amplitude spectrum. The effect of pulse on frequency content of motions was discussed on the light of this definition. The advantage and superior features of the new definition were related to the inelastic displacement ratio (IDR) for single-degree-of-freedom systems with period equal to one half of the threshold period. Analyses performed for the proposed period at three ductility levels u=2,4,6 were compared with the results obtained at half of pulse period derived from wavelet analysis, peak-point method and the peak of product of the velocity and the displacement response spectra (Sv x Sd). According to the results, pulse effects on inelastic displacement ratio seem to be more important when $\frac{T_p^*}{T}=2$ (T is the fundamental vibration period of system). The results showed that utilizing of the proposed definition could facilitate an enhanced understanding of pulse-like records features.

• 대한물리치료과학회지
• /
• 제7권2호
• /
• pp.663-682
• /
• 2000

The purpose of this study was to identify the superior exercise on the reduction of low back pain, between the Mckenzie exercise and the williams exercise. 24 chronic low back pain patients were randomly divided into 3 groups (Mckenzie exercise group = 8, williams exercise group = 8, control group = 8). Each group examined using the Borg scale in a reduction of low back pain, the EMG amplitude in a stationary sit-up position and in a stationary 1000 back extension position. The Results are as follow. 1. After the training period, the Mckenzie exercise group and the williams exercise group revealed reduction of low back pain, but the control group does not revealed it. 2. After the training period, there were no significant differences on the reduction of low back pain between the Mckenzie exercise group and the williams exercise group. 3. After the training period, no groups decreased on the abdominal muscle EMG amplitude. 4. After the training period, all groups revealed no significant differences on the abdominal muscle EMG amplitude. 5. After the training period, all groups decreased on the low back muscle EMG amplitude. 6. After the training period, all groups revealed no significant differences on the low back muscle EMG amplitude. Overall, the study suggested that the Mckenzie exercise and the williams exercise achieve the same effect on the reduction of low back pain, and the fact seems to be influenced by other factors without muscular adaptation.

• 한국안광학회지
• /
• 제15권1호
• /
• pp.73-78
• /
• 2010

목적: 조절능력의 변화가 빈번하게 발생되는 35세 이상 50세 미만을 대상으로 l차시기(08:00~10:00), 2차시기(13:00~15:00), 3차시기(18:00~20:00에 걸쳐 조정기능의 변화를 알아보고자 하였다. 방법: 104명의 피검사자를 비노안과 초기노안으로 분류하여 조절력과 조절용이성, 상대조절력을 검사하였다. 결과: 좌우안과 양안의 조절력을 비노안과 초기노안 모두 2차시기가 가장 높게 나타났으며, 초기노안용 일일변화에 유의성을 보였다. 조절용이성에서 비노안용 3차시기가, 초기노안용 2차시기가 가장 높았고, 변화에 대한 유의성이 모두 있는 것으로 나타났다. 허성상대 조절에 대한 일일변화에서 비노안, 초기노안 모두 l차시기가 가장 높았으며, 실성상대조절용 비노안, 초기노안 모두 2차시기가 가장 높았다. 결론: 초기노안에서 허성상대조절을 제외한 조절력, 조절용이성, 실성상대조절은 2차시기가 가장 높았다.

• Journal of Astronomy and Space Sciences
• /
• 제36권1호
• /
• pp.11-20
• /
• 2019

Being a torque free motion of the rotating Earth, Chandler wobble is the major component in the Earth's polar motion with amplitude about 0.05-0.2 arcsec and period about 430-435 days. Free core nutation, also called nearly diurnal free wobble, exists due to the elliptical core-mantle boundary in the Earth and takes almost the whole part of un-modelled variation of the Earth's pole in the celestial sphere beside precession and nutation. We hereby present a brief summary of their theories and report their recent features acquired from updated datasets (EOP C04 and ECMWF) by using Fourier transform, modelling, and wavelet analysis. Our new findings include (1) period-instability of free core nutation between 420 and 450 days as well as its large amplitude-variation, (2) re-determined Chandler period and its quality factor, (3) fast decrease in Chandler amplitude after 2010.

• Fisheries and Aquatic Sciences
• /
• 제17권1호
• /
• pp.145-153
• /
• 2014

The motion of the otter board on a trawl can affect the motion of trawl nets, and the motion of the codend can affect fish selectivity. Preliminary measurements of the tilt of bottom trawl gear were carried out to compare the tilts of the otter board and codend. The tilt of the otter board was measured by Vector and tilt at 1.5 m anterior to the end of the codend, and the middle upper panel was measured with a micro-DST-tilt logger. Tilt data such as yaw, pitch, and roll were analyzed by the fast Fourier transformation method and global wavelet and event analyses for the period or amplitude. The mean period ${\pm}$ standard deviation of the tilt in the otter board, $(5-6){\pm}2s$, was similar to the period of the codend, $(4-6){\pm}(2-3)s$, whereas the amplitude of the codend was greater than that of the otter board. The yaw and pitch periods were not significantly different between the otter board and codend, but roll was different. Furthermore, the tilt period frequencies of the otter board and codend were not significantly different. Accordingly, the tilt motion of the codend was mostly related to the tilt of the otter board.

• 한국안광학회지
• /
• 제16권1호
• /
• pp.75-81
• /
• 2011

목적: 38세 이상 50세 미만의 초기노안자 52명을 대상으로 1차시기(08:00~10:00), 2차시기(13:00~15:00), 3차시기(18:00~20:00)에 걸쳐 조절기능의 일일변화를 조사하였다. 방법: 초기노안자 52명(남 30명, 여 22명)을 근거리 작업량에 따라 4군(I군: ${\geq}$ 7 hrs~IV군: < 3 hrs)으로 분류하여 조절력, 조절용이성, 상대조절력을 검사하였다. 결과: 조절력은 하루 일과 중 근업이 가장 많은 I군에서 가장 낮은 것으로 측정되었고, 단안과 양안의 조절력은 I군~IV군 모두 2차시기의 조절력이 가장 높았다. 조절용이성에서 I군의 단안과 양안, II군의 단안 그리고 III군의 단안과 양안은 2차시기가 가장 높았고, II군의 양안과 IV군의 단안과 양안은 3차시기가 가장 높은 것으로 나타났다. 허성상대조절력은 I군~IV군 모두 1차시기가 가장 높았고, 실성상대조절력의 경우 I~III군은 2차시기가, IV군은 3차시기가 가장 높은 것으로 나타났다. 결론: 작업환경 및 시간은 조절기능에 영향을 줄 수 있으므로 초기노안자의 경우 하루 일과 중 업무 시간대를 고려하여 조절기능에 대한 검사를 하는 것이 안정피로 증상을 해소하는데 도움이 될 것이다.