• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1245-1249
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• 2017

Recently, unusual transformer failures have been reported in 25kV power systems connected with a VCB and transformer. In this study, performance of the protection system, dielectric strength of the transformers, characteristics of switching surges and resonance phenomena were analysed and assessed. All investigations regarding the insulation breakdown of the transformers were carried out by simulations, laboratory tests, factory tests and on-site measurements in order to thoroughly investigate the root causes. Furthermore, experimental methods for investigating the resonance phenomenon were derived and tests were conducted applying the derived method to recreate the phenomenon in the transformer. It is found that resonance between the transformer and switching surge generated by closing a VCB can initiate the breakdown of internal windings of a transformer.

• 한국전기전자재료학회논문지
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• 제22권2호
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• pp.142-150
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• 2009

We constructed a Class I flextensional transducer, and analyzed the variation of the resonance frequency of the transducer in relation to its structural and material variables. We used the FEM for the analysis. Total length of the transducer, thickness and material properties of the shell have large effects on the resonance frequency. While outer radius of the ceramic stack and material properties of the ceramic stack have no effect on the resonance frequency. In addition, the validation of the FE model was verified by manufacturing and comparison of the impedance analysis. Results of the present work can be utilized to design a Class I flextensional transducers of various resonance frequency.

• Investigative Magnetic Resonance Imaging
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• 제25권2호
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• pp.135-140
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• 2021

Breast angiosarcoma is a very rare manifestation. Herein, we report a case of breast angiosarcoma in a 21-year-old woman admitted to our hospital with a one-year history of a palpable mass with fullness and swelling of the right breast. The various imaging findings, including mammography, ultrasound (US), and magnetic resonance imaging (MRI), of this rare disease are described. The imaging findings of US and combined MRI of breast angiosarcoma were specific in this case. The imaging characteristics could be helpful in detecting and diagnosing breast angiosarcoma in young women with a palpable mass with fullness and swelling of the breast.

• 한국해양공학회지
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• 제35권3호
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• pp.216-228
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• 2021

In the present study, the performance of a floating oscillating water column (OWC) device has been studied in regular waves. The OWC model has the shape of a hollow cylinder. The linear potential theory is assumed, and a matched eigenfunction expansion method(MEEM) is applied for solving the diffraction and radiation problems. The radiation problem involves the radiation of waves by the heaving motion of a floating OWC device and the oscillating pressure in the air chamber. The characteristics of the exciting forces, hydrodynamic forces, flow rate, air pressure in the chamber, and heave motion response are investigated with various system parameters, such as the inner radius, draft of an OWC, and turbine constant. The efficiency of a floating OWC device is estimated in connection with the extracted wave power and capture width. Specifically, the piston-mode resonance in an internal fluid region plays an important role in the performance of a floating OWC device, along with the heave motion resonance. The developed prediction tool will help determine the various design parameters affecting the performance of a floating OWC device in waves.

• Structural Engineering and Mechanics
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• 제88권4호
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• pp.355-368
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• 2023

Employing the non-local strain gradient theory (NSGT), this paper investigates the nonlinear resonance characteristics of functionally graded material (FGM) nanoshells with initial geometric imperfection for the first time. The effective material properties of the porous FGM nanoshells with even distribution of porosities are estimated by a modified power-law model. With the guidance of Love's thin shell theory and considering initial geometric imperfection, the strain equations of the shells are obtained. In order to characterize the small-scale effect of the nanoshells, the nonlocal parameter and strain gradient parameter are introduced. Subsequently, the Euler-Lagrange principle was used to derive the motion equations. Considering three boundary conditions, the Galerkin principle combined with the modified Lindstedt Poincare (MLP) method are employed to discretize and solve the motion equations. Finally, the effects of initial geometric imperfection, functional gradient index, strain gradient parameters, non-local parameters and porosity volume fraction on the nonlinear resonance of the porous FGM nanoshells are examined.

• 한국포장학회지
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• 제12권2호
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• pp.97-102
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• 2006

Shock and vibration inputs are transmitted from the transporting vehicle through the packaging to the fruit. The vibration causes sustained bouncing of fruits against each other and the container wall. The steady state vibration input may cause serous fruit injury, and the damage is particularly severe if the fruits are bounced at its resonance frequency. The determination of the resonance frequencies of the fruits and vegetables may help the packaging designer to determine the proper packaging system providing adequate protection for the fruits, and to understand the complex interaction between the components of the fruits when they relate to expected transportation vibration inputs. To analyze the vibration properties of the watermelon for optimum packaging design during transportation, sinusoidal sweep vibration tests were carried out. The resonance frequency of the watermelon ranged from 19 to 32 Hz and the amplitude at resonance was between 1.6 and 2.9 G. The resonance frequency and amplitude at resonance frequency band of the watermelon decreased with the increase of the sample mass. The multiple nonlinear regression equation for predicting the resonance frequency of the watermelon were developed using the independent variables such as mass, input acceleration and sphericity.

• KEPCO Journal on Electric Power and Energy
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• 제1권1호
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• pp.1-8
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• 2015

When the line and switchgear of the substation system are disconnected, ferro-resonance can occur. This happens even if the capacitive reactance and inductive reactance are not equal, which are not common resonance conditions. Resonance conditions vary depending on the busbar configuration environment. Although the damping resistance method applying the existing saturable reactor to cope with ferro-resonance has been successfully applied on site, there can be loss of normal function during long-term operation. The reason is because the rise in the operating frequency of saturable reactors means the saturation number is increased. Therefore, it can no longer function as saturable reactor since the resistor having inadequate capacity is burned out. To address this problem, in this paper, an EMTP-based simulation test was performed by designing and applying a dual reactor method, which adds an extended divergence reactor to the 1st side of the VT. The test result confirms that when the divergence reactor is inserted, the voltage and current values obtained at the 1st side and 2nd side of the VT as well as current values of divergence reactor part were stabilized from the transient phenomena and return to normal values. When compared with existing measures, although this method is similar in adding having a reactor added to a system regarding ferro-resonance, it has the advantage of being able to prevent ferro-resonance in advance since the reactor is added before the system is saturated. In addition, because it does not use damping resistance, it can extend the equipment life and stabilize its operation. Therefore, there are a lot of differences in terms of its operating characteristics and achivement of goal between the conventional method and new divergence reactor method.

• Clinics in Shoulder and Elbow
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• 제18권4호
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• pp.211-216
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• 2015

Background: Few studies have investigated magnetic resonance (MR) characteristics of traumatic posterosuperior rotator cuff tears involving the supraspinatus and infraspinatus. We hypothesized that traumatic rotator cuff tears may have MR characteristics distinguishable from those of non-traumatic tears. Methods: Preoperative MR arthrography and intraoperative tear size measurements were compared in 302 patients who underwent MR arthrography and subsequent arthroscopic rotator cuff repairs for traumatic (group T, 61 patients) or non-traumatic (group NT, 241 patients) tears. The inclusion criteria for both groups were posterosuperior full-thickness rotator cuff tear and age between 40 and 60 years. For group T, traumas were limited to accidental falls or slips, or sports injuries, motor vehicle accidents; injuries were associated with acute onset of pain followed by functional shoulder impairment; and time between injury and magnetic resonance imaging (MRI) was 6 weeks or less. Results: In group T, 72.1% of shoulders (44 patients) had tendon tears with blunt edges while 27.9% of shoulders (17 patients) had tears with tapering edges. In contrast, 21.2% of patients in group NT (51 patients) had blunt-edge tears, while 78.8% (190 patients) of tears had tapering edges. These results were statistically significant (p<0.001) and estimated odds ratio was 9.6. The size of tear did not vary significantly between groups. Conclusions: We found no exclusive MR characteristic to define traumatic tears. However, oblique coronal MRI of traumatic tears showed a significant tendency for abrupt and rough torn tendon edges and relatively consistent tendon thicknesses (without lateral tapering) compared to non-traumatic cuff tears.

• 한국항공우주학회지
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• 제45권4호
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• pp.328-341
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• 2017

발사체의 추력벡터제어를 위한 구동장치시스템에서 관성부하를 갖는 전기기계식 위치서보 시스템의 공진 특성과 유연한 기체구조체 지지부의 구조공진이 결합되어 합성공진이 발생한다. 이렇게 발생한 공진은 발사체의 자세제어시스템에 되먹임되어 자세안정성에 영향을 줄 수 있다. 본 논문에서는 발사체의 추력벡터제어를 위한 직구동 방식의 전기기계식 구동장치의 합성공진을 해석하기 위한 모델을 소개하고 합성공진 현상을 저감하여 구동기의 동특성을 개선하는 동적 하중 되먹임 제어기법의 해석 및 시험 결과를 기술하였다.

• 마이크로전자및패키징학회지
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• 제10권1호
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• pp.65-69
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• 2003

소결온도에 따른 아이솔레이터/서클레이터용 (Y, Ca)-(Fe, V, In, Al)-O 계 YIG 페라이트의 미세구조와 전자기적 특성을 고찰하였다. $Y_{2.1}Ca_{0.9}Fe_{4.4}V_{0.5}In_{0.05}Al_{0.05}O_{12}$ 조성의 시편들을 일반적인 세라믹 제조 공정에 따라 $1300^{\circ}C$, $1330^{\circ}C$, $1350^{\circ}C$, $1370^{\circ}C$에서 각각 소결하였다. 소결체는 XRD를 이용하여 상분석을 실시하였고, SEM을 이용하여 미세구조를 관찰하였다. VSM을 이용하여 포화자화값$(4{\pi}M_s)$을 측정하였으며, FMR(Ferromagnetic Resonance)실험으로 자기공명반치폭$({\Delta}H)$을 측정하였다. YIG 페라이트의 마이크로파 특성은 Network Analyzer를 이용하여 측정하였다. $Y_{2.1}Ca_{0.9}Fe_{4.4}V_{0.5}In_{0.05}Al_{0.05}O_{12}$ 조성의 YIG 페라이트는 $1350^{\circ}C$에서 소결시 가장 높은 밀도값과 포화 자화$(4{\pi}M_s)$ 값을 나타내었고, 가장 낮은 자기 공명 반치폭$({\Delta}H)$ 값을 나타내었다.