• 산업공학
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• 제14권1호
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• pp.106-110
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• 2001

The importance of development of occupational safety index is truly great. It will contribute to the wise direction of safety program. In present, frequency and severity ratios were the standard measure. These terms express the incidence of major injuries and severity of the major injuries experience, each with relation to the employee-hours of work exposure during the period that is measured. But these measure don't expressed the dangerous feeling degree of worker. In this study, Effective Industrial Safety Index(EISI) was developed using dangerous feeling degree of worker, frequency of injuries, and severity of injury. EISI can be used as an aid for effective safety management in workplace.

• 대한토목학회논문집
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• 제31권2B호
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• pp.87-98
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• 2011

최근 지구온난화에 따른 기후변화로 홍수와 가뭄 같은 수문학적 재해가 과거에 비해 발생빈도와 크기가 변하고 있는 추세이다. 특히 가뭄은 긴 지속기간에 걸쳐 피해를 유발하므로 다른 수문학적 재해에 비해 보다 심각한 결과를 초래한다. 하지만 역설적으로 가뭄은 홍수와 달리 장기간에 거쳐 발생하므로 중요성과 심각성을 인식하기 어렵다. 따라서 가뭄의 발생에 대해 분석하고 그에 대한 대책을 마련하기 위해 여러 가지 가뭄의 종류 중 강수량과 가장 밀접한 관련이 있는 기상학적 가뭄에 대해 분석을 실시했다. 기상청에서 관측한 강수 및 온도자료를 이용하여 기상학적 가뭄지수인 팔머가뭄심도지수(Palmer Drought Severity Index), 표준강수지수(Standard Precipitation Index), EDI(Effective Drought Index)를 산정하였다. 그리고 산정된 가뭄지수를 비교분석하여, 실제 과거가뭄사상에 잘 부합되며, 일별로 지수 산정이 가능한 장점이 있는 EDI를 이용해 가뭄빈도해석을 실시하였다. 분석방법으로는 경계핵밀도함수를 이용해 EDI의 빈도해석을 실시하였다. 분석 결과, 대부분의 지점에서 봄철의 가뭄재현기간이 10년에서 20년 빈도 사이의 값을 나타내 다른 계절보다 봄에 가뭄이 잦음을 확인할 수 있었다. 또 영남지방과 남해안 일대의 재현기간이 상대적으로 더 짧게 나타나 지역적으로도 가뭄의 심도와 재현기간에 차이가 있음이 확인되었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.971-977
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• 2005

Power Flow Analysis (PFA) is developed for the effective predictions of frequency-averaged vibrational response in medium-to-high frequency ranges. In PFA, the power coefficients of semi-infinite structure and for-field energy density are used to predict the vibrational responses of structures. Generally, at high frequencies, PFA can predict narrow-band frequency-averaged vibrational responses of built-up structures. However, in low- to medium frequency ranges, the dynamic responses obtained by PFA represent broad-band frequency-averaged vibrational energy densities. For the prediction of vibrational response variance in Power Flow Finite Element Method (PFFEM), the variances of input power and joint element matrix describing structural coupling relationship are derived. Finally, for the validity of developed formulation, numerical examples for two co-planer plates are performed and the vibrational response variance of the structure are compared with the results of classical and PFFEM solutions.

• 한국군사과학기술학회지
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• 제14권5호
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• pp.818-824
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• 2011

In this paper, we proposed a phase noise model of a frequency synthesizer for a radar system. Especially, it was proposed a phase noise model in a DAS(Direct Analog Synthesizer) and a frequency up converter system using Leeson's model. The proposed phase noise model was derived from the measurement data of model 1 and evaluated by adapting to model 2 and model 3 frequency synthesizers. The prediction phase noise by modeling was totally matched to the measured data and the effective analysis of the phase noise was done in a frequency synthesizer and a frequency converter of radar system.

• Structural Engineering and Mechanics
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• 제49권3호
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• pp.411-425
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• 2014

This paper presents the processing of nonlinear features associated with a damage event by quadratic time-frequency distributions for damage identification in a frame structure. A time-frequency distribution is a function which distributes the total energy of a signal at a particular time and frequency point. As the occurrence of damage often gives rise to non-stationary, nonlinear structural behavior, simultaneous representation of the dynamic response in the time-frequency plane offers valuable insight for damage detection. The applicability of the bilinear time-frequency distributions of the Cohen class is examined for the damage assessment of a frame structure from the simulated acceleration data. It is shown that the changes in instantaneous energy of the dynamic response could be a good damage indicator. Presence and location of damage can be identified using Choi-Williams distribution when damping is ignored. However, in the presence of damping the Page distribution is more effective and offers better readability for structural damage detection.

• Structural Engineering and Mechanics
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• 제48권4호
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• pp.455-466
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• 2013

In recent years, many countries have added railway noise to the issues covered by noise regulations. It is known that the rail is the dominant source of rolling noise at frequency range of 500Hz-2000Hz for the conventional speeds (<160km/h). One of the effective ways to reduce noise from railway track is using a rail vibration absorber. To study the acoustic performance of rail absorber, the decay rates of vibration have long been used by researcher. In this paper, A FE model of a periodic supported rail with infinite element in ABAQUS is developed to study the acoustic performance of the rail absorber. To compute the decay rates, acceleration responses along the rail transferred to MATLAB to obtain response levels in frequency domain and then by processing the response levels, the decay rates obtained for each1/3octav band. Continous rail absorber is represented by a steel layer and an elastomer layer. The decay rates for conventional rail and rail with one-side absorber and also, the rail with two side absorber are obtained and compared. Then, to improve the system of rail absorber, a steel plate with elastomer layer is added to bottom of the rail foot. The vertical decay rate results show that the decay rate of rail vibration along the track is significantly increased around the tuned frequency of the absorber and thus the rail vibration energy is substantially reduced in the corresponding frequency region and also effective in rail noise reduction.

• The Journal of Korean Physical Therapy
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• 제25권5호
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• pp.316-321
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• 2013

Purpose: The aimed of this study was to investigate muscle activation related to postural stability according to different frequency of whole body vibration during quiet standing, to identify the most effective training conditions that cause the highest neuromuscular responses, and to evaluate the difference of EMG activation according to the anatomical position of the muscle - proximal or distal from the vibration platform. Methods: Eighteen healthy subjects voluntarily participated in this single-group, repeated-measures study in which EMG data from upper trapezius, rectus abdominalis, external oblique abdominalis, elector spinae, gluteus maximus, rectus femoris, semitendinosus, and gastrocnemius were collected over different frequencies (0-5-10-15-20-25Hz) for each subject during quiet standing. Results: We observed a statistically significant difference in the mean values of %RVC of muscular activation according to different frequencies of whole body vibration during quiet standing in all muscles (p<0.05). Conclusion: Our results indicate that lower frequencies of vibration result in low muscular activation, and higher frequencies elicit high muscular activation. However, the most effective training condition that caused the highest activation was 20 Hz. In addition, the proximally located lower extremity muscles (GCM, RF, ST, GM) showed higher activation than the distally located trunk and neck muscles (ES, EO, RA, UT) together with increasing frequency.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.2009_2010
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• 2009

Thin-gauged 3% Si-Fe sheets having a high magnetic induction of over 1.9 T have been developed for the purpose of applications where operation frequency is higher than power frequency. In order to clarify requirements of iron loss characteristics for the applications, iron loss characteristics of the newly developed strip were investigated by iron loss separation method and were compared with those of commercially produced 0.3 mm-thick electrical sheets. In case of relatively high excitation induction(1.7 T) and low frequency(60 Hz), reducing hysteresis loss is effective to decrease total iron loss. In case of relatively low excitation induction(1.0 T) and high frequency(1 kHz), reducing eddy-current loss is effective by decreasing thickness and grain size to improve total iron loss.

• 제어로봇시스템학회논문지
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• 제5권8호
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• pp.977-989
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• 1999

The purpose of this study is to analyze how the human body having more muscles than its degree-of-freedom modulates an effective stiffness using redundant actuation, and to apply this concept to the design and control of advanced machines which requires adaptable spring. To investigate the adaptable stiffness phenomenon due to redundant actuation in the human body, this paper derives a general stiffness model of the Human body. In particular, for a planar 1 DOF human arm model, a planar 2 DOF human arm model, a spherical 3 DOF shoulder model, a 4 DOF human arm model, and a 7 DOF human arm model, the required nonlinear geometry ad the number of required actuator for successful modulation of the effective stiffness are analyzed along with a load distribution method for modulation of the required stiffness of such systems. Secondly, the concept of motion frequency modulation is introduced to show the usefulness of adaptive stiffness modulation. The motion frequency modulation represents a control of stiffness and / or inertia properties of systems. To show the effectiveness of the proposed algorithm, simulations are performed for 2 DOF anthropomorphic robot.

• Smart Structures and Systems
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• 제21권5호
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• pp.583-590
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• 2018

Nowadays, many tunnels have been commissioned for several decades, which require effective inspection methods to assess their health conditions. The ambient vibration test has been widely adopted for the damage identification of concrete structures. In this study, the vibration characters of tunnel lining shells built with forepoling method was analyzed based on the analytical solutions of the Donnell-Mushtari shell theory. The broken rock, foreploing, rock-concrete contacts between rock mass and concrete lining, was represented by elastic boundaries with normal and shear stiffness. The stiffness of weak contacts has significant effects on the natural frequency of tunnel lining. Numerical simulations were also carried out to compare with the results of the analytical methods, showing that even though the low nature frequency is difficult to distinguish, the presented approach is convenient, effective and accurate to estimate the natural frequency of tunnel linings. Influences of the void, the lining thickness and the concrete type on natural frequencies were evaluated.