• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.71-71
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• 2004

일반적으로 동흡진기는 하나의 가진진동수에 의해 진동하는 감쇠가 작은 기계나 구조물에 효과적으로 적용되고 있다 대부분의 동흡진기의 적용 사례는 주 진동이 유발되는 부위, 또는 진동을 억제해야하는 부위에 직접적으로 동흡진기를 부가하여 효과를 얻는 방식을 택하고 있다. 그러나 절연기를 설치 할 수 없는 경우라든지, 절연기로는 한계가 있는 경우, 이미 설치가 완료된 기계 시스템에 절연 변경이 곤란한 경우 또는 국부 진동모드에 대한 진동저감을 할 때는 동흡진기에 대해 보다 일반적인 접근 방법이 필요하며 질량과 스프링계를 부착하기 힘든 경우나 억제시키려는 부위에 설비나 기기의 성능을 저해할 수 있는 경우에는 부득이 그 위치를 변경시켜 줘야 할 경우가 생긴다 할 수 있다.(중략)

• The Journal of the Acoustical Society of Korea
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• v.8 no.1
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• pp.31-37
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• 1989

The effectiveness of using a composite beam with constrained visco-elastic layer as a dynamic vibration absorber is investigated. The performance of this absorber is evaluated in terms of displacement transmissibility when to a primary beam with built-in ends and compared to that of the uniform beam absorber. The results of analysis and design show that it is possible to suppress simultaneoulsy the peak transmissibilities at two or more resonance frequencies and the optimal parameters are located within the available viscoelastic material properties.

• The Journal of Engineering Geology
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• v.4 no.2
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• pp.207-218
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• 1994

The natural constants of moving coil type geophone can be determined by free impedance and step force method. The former method was desirable for the measurement of natural frequency($f_o$), inertial mass(m) and damping factor($h_o$), but the latter method for sensitivity(G). In particular, the value by the latter method should be corrected for the noise by the long period movement of measurement device. The results of frequency characteristics from these constants operate the accelerometer and displacement system in the boundary of natural frequency.

• Geophysics and Geophysical Exploration
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• v.19 no.3
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• pp.164-173
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• 2016

Cable-free seismic technology is to acquire seismic data with independent receivers which are not connected by cables. This is an effective method for survey designs with less topographical conditions. With technology advancement for cable-free receivers, reliable data quality, easy deployment, and picking up the receivers, the cable-free technology has begun to apply to land seismic acquisition. In this study we introduced a cable-free seismic system and its equipment. We tried to build up the cable-free seismic technology through the field application. In the seismic tomography field applications, the seismic signals of the cable-free receiver and cabled receiver with the same distance from the source show the same phase in early stage. The difference of the first arrival times between two signals is less than 0.4 ms, which could be accepted. In the field application for seismic reflection exploration, we acquired shot gathers with different source depth and dynamite charge. The shot gathers from cable-free and cabled system are similar to each other. With an efficient method for receiver deployment and survey design, the application of the cable-free technology will increase.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1992.10a
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• pp.55-58
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• 1992

일반적으로 기계계 또는 기계요소가 외력을 받아 진동할 때 공진이 문제시 되는 경우가 많다. 이러한 계의 공진 제어에는 주로 댐핑재료(damping material)의 사용이 일반화 되어왔다. 그러나 댐핑재료를 사용한 제어에 있어 서는 계의 특성이나 규모등에 따라 많은 제한요소가 따르는데 특히 구조물 의 규모가 커지거나 복잡해지면, 제어 위치선정에도 어려움이 따르며 그 효 과도 기대하기 어렵다. 다른 방법으로는 기계계의 동적 특성치에 변화를 주 는 것이나, 이를 허용하지 않는 계가 많다. 따라서 이러한 단점들을 보완하 기 위해서 고안된 것이 동흡진기(dynamic absorber)이다. 기존의 선형 동흡 진기[1]는 주공진 부근영역에서 가진되는 계에만 적용이 가능하기 때문에, 흡진기와 기계계의 크기비(ratio)의 결정이 제한적이다. 이런 제한을 극복하 여 비교적 넓은 범위의 가진 주파수에 대해서 최대의 응답을 최소화하기 위 해서는 비선형 동흡진기[5]의 해석이 요구되고 있다. 제어대상의 최적응답을 얻기 위해 흡진기의 크기를 변화시키는 과정을 tuning이라 하는데, 이 과정 을 통해 최적의 감쇠값을 결정할 수 있다. 비선형 흡진기의 장점은 tuning 과정시 비선형 파라미터 변화에 의해 제어가 가능한 영역을 확장할 수 있다. 따라서 본 연구에서는 동흡진기의 tuning 과정시 흡진기의 크기비와 비선형 파라미터비에 따른 효과를 정규모우드를 활용하여 고찰한 후, 최적의 응답을 통해 비선형 동흡진기의 동적 거동을 연구하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4473-4482
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• 2010

The examination of pulse, which is a typical palpation technique in the oriental medicine, has been used conventional analog system for discrimination of 28 pulses. However, the clipping phenomenon in the pulses, which used same feature extraction technique with ECG signals, has been occurred in analog system due to feature extraction method and over amplification from the input signals. It caused inaccurate to analyze the pulse signals. In this paper, we propose a digital filter design technique based on Prony's method for signal modeling and C-spline interpolation for feature extraction from pulse signal to compensate analog pulse detection system. In addition, we suggest a compensated electronic pulse detection system comprising new pulse analyzing algorithm and shape analysis technique for pulses, which were difficult to use in analog system. The feasibility for new proposed system has been confirmed comparing output signals between electronic pulse detection system having proposed filter design techniques with pulse analyzing algorithm and conventional analog system.

• Journal of the Korean earth science society
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• v.32 no.6
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• pp.674-686
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• 2011

Choosing a seismic source and geophone type including a coupling method can be the most important factor in shallow seismic surveys. We studied the characteristics of seismic signals by analyzing 6 different seismic data sets that collected from several sources and geophone conditions. Geophones attached to weight plate (1.8 kg) can be easily and economically installed on the paved road where geophones with spikes would cause the coupling problem. In addition, experiments in this study revealed that a small handy hammer can be used as a seismic source by striking the paved road to generate the seismic signals within 200 ms two-way travel time. Attaching weight plates to geophones may change the geophone response curve which generally depends on the geophone mass, but the change seems not to give significant differences in the first arrival of refracted wave and in the pattern of reflection events. Consequently, using weight plates on paved roads can be an efficient and cost-saving method in the near-surface high-resolution seismic surveys.

• Geophysics and Geophysical Exploration
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• v.6 no.3
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• pp.153-159
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• 2003

Using reciprocity theorem, one direction aperture of seismogram can be extended to full aperture seismogram. Modified seismogram is applied to reverse time migration only to acquire improved migration image. In this paper, we tested reverse time migration with the Marmousi velocity data to examine efficiency of modified seismogram. And linearly increasing velocity model is selected and examined for a case where velocity data is insufficient. When true velocity is applied, using modified seismogram enhances the reverse time migration image more than using original seismogram. In the case of using linearly increasing velocity model, migration image is distorted. So low frequency source is brought in migration process. Reverse time migration image with low frequency source and linearly increasing velocity model is improved when modified seismogram is used. From the result of study, seismogram modification by reciprocity theorem is useful and migration image can be enhanced.

• Journal of the Korean Society of Mineral and Energy Resources Engineers
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• v.55 no.6
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• pp.635-648
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• 2018

This study analyzed patent trends of seismic nodal systems and the technical characteristics of core patents of three major companies, including Fairfield, Sercel, and Wireless Seismic, to examine the focus of technology development of each company. From the analysis, the patent application growth rate of seismic nodal systems has steadily increased since early to mid-2000s and has recently shown a higher growth rate. Over the same period, the patent application growth rate of the three major companies examined was higher than that of the global trend, and patent infringement cases was also examined to evaluate market competition in this field. Analysis of the technical characteristics of the three companies' 33 core patents showed that they are generally focused on seismic signal detection. Sub-technologies included improved reliability of data acquisition, data transmission efficiency, and overall operating of the seismic nodal system. New entrants in field of technology development or manufacturing of seismic nodal systems where the market is growing must closely analyze the contents of major companies' products and patents to prevent possible patent disputes or duplicate research.

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.180-183
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• 1999

A proto-type seismic measurement system with a reference was developed to improve S/N (signal-to-noise ratio) of seismic data, especially in noisy urban areas. Two pairs of correlation measurements (the one for microphone and geophone, and another for electromagnetic (EM) loop and geophone) were carried out near Kimpo Airport and at Kimje. The spectrum analyses were also performed to investigate the correlation of two pairs of time series; one for microphone and geophone, and another for EM loop and geophone. The sound waves measured with the microphone and the geophone are highly correlated. However, differences in the reponses are readily identifiable across 200 Hz; in the vicinity of 100 Hz, the spectral energy for geophone is 20 dB higher than that for microphone, and at near 500 Hz, the spectral energy for microphone is 30 dB higher than that for geophone. Overall, the spectral energy appears concentrated on the frequency window below 600 Hz for geophone. It contrasts with the observation of dominant frequency at the range of above 200 Hz for microphone. The wave forms of EM noise (due to an ACDC inverter) measured with EM loop and geophone are consistently and highly correlated each other. The power spectrum of the EM noise for EM loop shows that the spectral energies at odd harmonic frequencies of 60 Hz are higher than those at even harmonic frequencies of 60 Hz. It is compared to the power spectrum for geophone; the spectral energies at odd harmonics are nearly same as those at even harmonic frequencies.