• 동력기계공학회지
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• 제14권4호
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• pp.63-67
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• 2010

This paper introduces the eddy current signal characteristic of magnetic and non-magnetic gas turbine rotor. In the past, Magnetic particle inspection method was used in magnetic material for qualitative defect evaluation and the ultrasonic test method was used for quantitative evaluation. Nowadays, eddy current method is used in magnetic gas turbine rotor inspection due to advanced sensor design technology. We are studying on the magnetic gas turbine rotor by using eddy current method. We prepared diverse depth specimens made by magnetic and non-magnetic materials. We select optimum frequency according to material standard penetration data and experiment results. We got the signal on magnetic and non-magnetic material about 0.2 mm, 05 mm, 1.0 mm, 1.5 mm 2.0 mm and 2.5 mm depth defects and compare the signal amplitude and signal trend according to defect depth and frequency. The results show that signal amplitudes of magnetic are bigger than non-magnetic material and the trends are similar on every defect depth and frequency. The detection and resolution capabilities of eddy current are more effective in magnetic material than in non-magnetic materials. So, the eddy current method is effective inspection method on magnetic gas turbine rotor. And it has the merits of time saving and simple procedure by elimination of the ultrasonic inspection in traditional inspection method.

• 대한기계학회논문집
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• 제17권9호
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• pp.2145-2152
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• 1993

The objective of this paper is to examine the detection limit, growth characteristics and notch curvature radius in short crack problem. Measurement techniques such as ultrasonic method and back-face strain compliance method were adopted. The fatigue crack growth rate of the short crack is slower than that of a long crack for a notched specimen. The characteristic of crack growth and crack closure is same as the case of a delay of crack growth caused by constant amplitude load for an ideal crack or single peak overload for a fatigue crack. The short crack is detected effectively by ultrasonic method. A short surface crack occurs in the middle of specimen thickness and is transient to a through crack depth is larger than the notch curvature radius.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권4호
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• pp.189-194
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• 2006

Dam jerk causes a chronic stomach disorder. The number of the patient of the Dam jerk increase in these days. However, there are no objective and quantitative study for a diagnosis of Dam jerk. Therefore, we designed diagnosis system using ultrasonic response signal for a diagnosis of Dam jerk. It was used to collect the response signal that is reflected at Dam jerk region of the abdominal. And then, the response signal at the Dam jerk region is 20% higher than the normal region. In the result. we could prove the reliability of the system.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
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• pp.146-149
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• 2003

To control the position, velocity and torque of the ultrasonic motor, a great variety of method are proposed such as the amplitude, phase difference, frequency and so on. In the case of phase difference method, it has some advantages: it can control the direction and velocity of rotation only adjusting the phase difference and it has wide control-band. During the USM driving on adjusting phase difference, its characteristic was transformed by the change of resonance-frequency of stator, which means that the resonance frequency is different according to the phase difference. Consequently, we need to set up the most suitable driving frequency according to each phase difference.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2007년도 춘계학술발표논문집
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• pp.287-290
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• 2007

We investigated the effect of ultrasound on the dewaterability of sewage sludge. Because, dewatering and disposal of waste sludge is a major economical factor in the operation of wastewater treatment plants. Capillary Suction Time(CST) and Specific Resistance to Filtration (SRF) were used to evaluate the sludge dewatering behaviors. From the results of the experiment, it was found that ultrasonic treatment can improve the dewaterability. We discovered that CST and SRF were highly related, according to the correlation coefficient($R^{2}$).

• 동력기계공학회지
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• 제14권2호
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• pp.65-70
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• 2010

Retaining rings are used to support the field winding end turns from the centrifugal force by the high speed of the field and these are the overstressed parts among the generator parts. There have been several retaining failures in Europe and America, all attributable to stress corrosion cracking in 18Mn-5Cr steel. Since then, each manufacture companies have developed a good 18Mn-5Cr steel in temperature, strength characteristic and it is used in many field now. From many findings and test results, we could conformed that the failure might be grown in the overstressed condition unrelated to the moisture particle.

• 대한의용생체공학회:의공학회지
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• 제5권1호
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• pp.55-62
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• 1984

A digital spectrum analysis technique was used to estimate the tissue characteristic parameters (transmission velocity and attenuation coefficient) in the phantom study and the human liver's ultrasound scanning. The soft tissue equivalent phantom was made with the combination materials of agar, water, powdered graphite, and n-propyl alcohol. In the human study, twenty five normal subjects and three patients with liver diseases were studied using the ultrasonic reflection signals and the spectrum analysis method The following results were obtained; 1. The soft tissue-equivalent materical could be produced with various acoustic parameters by changing the composition amount of the powdered graphite and n-propyl alcohol. 2. Attenuation coefficients of normal human liver tissue were estimated to be 0. 36 dB/cm MHz$\pm$0.11. In patients with liver disese, tile attenuation coefficients were shown to be different from the above normal values.

• 한국정밀공학회지
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• 제16권6호
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• pp.108-113
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• 1999

For cylindrical shells, the closed-form solutions are confined to the specific boundary and/or loading conditions. Though the finite element method is certainly a powerful solution approach for the structural dynamics problems, it has been well known to provide the solution reliable only in the low frequency region due to the inherent high sensitivities of structual and numerical modeling errors. Instead, the spectral element method has been proved to provide accurate dynamic characteristics of a structure even at the ultrasonic frequency region. Since the wave characteristic of a cylindrical shell becomes identical to that fo a flat plate as the frequency increases, an equivalent plate model (EPM) representing the high-frequency dynamic characteristics of the cylindrical shell is introduced herein. The EPM-based spectral element analysis solutions are compared with the known analytical solutions for the cylindrical shells to confirm the validity of the present modeling approach.

• Korea-Australia Rheology Journal
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• 제19권1호
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• pp.1-5
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• 2007

By combining ultrasonic energy which is essential for the chain scission of polymer molecules and a multifunctional agent (MFA) having double bonds at its ends, we were able to modify the molecular structure of polycarbonate (PC) from linear to a branched structure during melt processing. The three double bonds in chain ends of MFA were expected to act as sites for trapping macroradicals of PC during the course of ultrasound-assisted mixing process. The transformation of molecular structure of PC was confirmed by the measurements of rheological properties of the modified PC. After the ultrasonic irradiation of PC together with MFA, increase in complex viscosities and shear-thinning behavior were observed. The Cole-Cole plot and measurement of extensional viscosities revealed the characteristic features of branched structure with well-defined extensional behavior which is comparable to that of a commercial branched PC.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2277-2279
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• 1999

We have investigated the characteristic analysis of ultrasonic in case of occurring partial discharge in experimental steel chamber. This study presents the discriminative method of partial discharge by optimum threshold value. We have carried out the experiments of measuring partial discharge numbers between ultrasonic sensor and transducer with changing distance and barrier inside steel chamber. After the measured data were trasformed A/D conversion by GPIB, we used the optimum method of threshold value for counting numbers of partial discharge.