• Geomechanics and Engineering
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• 제28권1호
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• pp.77-87
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• 2022

Many geotechnical analyses require the investigation of water flow within partially saturated soil zone to incorporate the effect of climatic conditions. It is widely understood that the hydraulic properties of the partially saturated soil should be included in the transient seepage analyses. However, the characteristics of dual porosity soils with dual-mode water retention curve are normally modelled using single-mode mathematical equation for simplification of the analysis. In reality, the rainwater flow can be affected significantly by the dual-mode hydraulic properties of the soil. This paper presents the variations of safety factor for dual porosity soil slope with dual-mode water retention curve and dual-mode unsaturated permeability. This paper includes the development of the new dual-mode unsaturated permeability to represent the characteristics of soil with the dual-mode water retention curve. The finite element analyses were conducted to examine the role of dual-mode water retention curve and dual-mode unsaturated permeability on the variations of safety factor under rainfall loading. The results indicate that the safety factor variations of dual porosity soil slope modelled using the dual-mode water retention curve and the unsaturated permeability equation are lower than those of dual porosity slope modelled using single-mode water retention curve and unsaturated permeability equations.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.167-171
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• 2003

Acoustic characteristics of baffled combustion chamber to elucidate suppressing effect of baffle on combustion instability are numerically investigated by linear acoustic analysis. A hub-blade baffle of 5 blades is selected as a candidate one and five variants of baffles with various configuration are designed. Resonant-frequency shift and damping factor are analyzed quantitatively as damping parameters. When the hub is located radially at the pressure node, the decrease of resonant frequency and increase of damping factor in 1R mode are dominant. But sub-1T mode is formed within hub, therefore, there would be a possibility of initiating 1T mode in unbaffled region, which would occur another problem. For smaller hub size, four kinds of axial baffle length is selected. As the axial baffle length increases, resonant frequency shift and increase of damping factor of transverse acoustic modes is obtained. Especially, two close acoustic modes such as 1L and 1T could be overlapped for a certain axial length, resulting in extreme increase of damping factor. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.

• Journal of Electrical Engineering and Technology
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• 제5권3호
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• pp.468-476
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• 2010

This paper presents a direct single-stage power converter using single-phase isolated full-bridge converter modules, with inherent power factor correction (PFC) for a 12 kW switched mode power supply (SMPS). The advantages of the proposed converter are its simple control strategy, reduction in number of conversion stage, low input line current harmonics, and improvement in power factor. Analysis of the single-stage converter is carried out in continuous conduction mode of operation. Steady-state analysis of the proposed converter is conducted to obtain converter parameters. A systematic design procedure is also presented for a 12k W converter with a design example. The effect of load variation on SMPS is also studied in order to demonstrate the effectiveness of the proposed converter for the complete range of load conditions. A set of power quality indices on input ac mains for an SMPS fed from a single-stage converter is also presented for easy comparison of their performance.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.1123-1125
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• 2002

In this paper, interleaved boost converter is applied as a pre-regulator in switch mode power supply. Interleaved Boost Power Factor Preregulator (IBPFP) can reduce input current ripple as a simple voltage control loop only without inner current loop, because input current is divided each 50% by two switching devices. IBPFP can be classified as three cases from duty ratio condition in continuous current mode and be carried out state space averaging small signal modeling. According to modeling, the PID controller is applied and voltage control loop is constructed for suitable design condition. From frequency domain analysis, it is verified that control system is satisfied with design condition of switch mode power supply.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.167-170
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• 2000

The flexural vibration of a sandwich beam with partially inserted viscoelastic layer has been studied using the finite element analysis in combination with an experiment. Effects of length and thickness of partial viscoelastic layers on system loss factor(${\eta}_s$) and resonant frequency(${\omega}_r$) were considerably large. The thicker the viscoelastic layer in a sandwich beam, the larger the system loss factor in Mode 1 as compared with that in Mode 2. The loss factor increased almost linearly with increasing the length of partial viscoelastic layer. Effects of thickness of beams were also considered.

• 전력전자학회논문지
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• 제19권4호
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• pp.349-356
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• 2014

As the turns ratio of the tapped-inductor contributes to the step-up ratio, the tapped-inductor boost (TIB) converter has significantly increased level of difficulties in its analysis and design compared to the conventional boost converter where the duty ratio is the sole factor affecting the step-up ratio. In this paper, the operation of the continuous current mode TIB converter is briefly reviewed, the characteristics are analyzed in detail, and a design guideline optimizing the loss in the tapped-inductor is presented with a practical design example. Finally, experimental results from a 12V/120V prototype for 0.25A LED driver application are also presented to confirm the design.

• 한국산학기술학회논문지
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• 제20권1호
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• pp.189-199
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• 2019

본 연구의 목적은 축산차량의 이동이 빈번하게 일어나는 공간적 범위(방역권역)를 도출하는 것을 목적으로 한다. 이를 위하여 본 연구는 KAHIS에서 제공하는 축산차량의 시설 진입자료 중에서 6개 시점의 자료를 활용하였다. 이 자료를 축산시설간의 차량이동자료로 변환하고, 이를 행정구역단위로 취합하여 행정구역간의 OD자료를 구축하였다. 구축된 OD 자료를 활용한 R-mode 요인분석을 실시하여 동일요인으로 추출된 지역을 하나의 권역으로 판단하였다. 분석결과를 정리하면 다음과 같다. 첫째, 6개 시점 자료의 요인분석을 실시한 결과 16개~18개의 요인이 도출되었으며, 도출된 요인은 전체 분산의 63~68%를 설명하였다. 두 번째, 도출된 요인을 바탕으로 지역을 구분한 결과, 전남남해안지역, 전남지역, 전북지역, 충남서해안지역, 경남지역, 경북북부지역, 영남동해안지역은 시점에 따른 변화가 적은 안정적인 지역으로 나타났다. 반면, 충북지역, 강원도지역, 수도권지역은 상대적으로 변화가 큰 지역이다. 세 번째, 6개 시점의 자료를 종합하여 강원권역, 경기남부권역, 경기북부권역, 경남권역, 경북남부권역, 경북북부권역, 남해안권역, 대전권역, 동해안권역, 전남권역, 전북권역, 충남권역, 충북권역의 13개 권역을 도출하였다.

• Journal of the Optical Society of Korea
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• 제18권6호
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• pp.650-656
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• 2014

We propose a novel active fiber design for selectively generating cylindrical vector beams (CVBs) or cylindrical vector modes (CVMs) which can be applied to conventional fiber lasers. A fiber is designed to have a ring-shaped core refractive index profile which can lead to the best overlap between the active dopant distribution profile and the lowest-order CVM (LCVM) field profile. Therefore, the overlap factor (OVF) of the LCVM becomes even higher than that of the fundamental mode. We emphasize that this condition cannot be satisfied by a conventional step-index core fiber (SICF) but by the ring-doped core fiber (RDCF). Because the lasing threshold is inversely proportional to the OVF, the LCVM can predominantly be stimulated even without going through special procedures to impose extra loss mechanisms to the fundamental mode. We numerically verify that the OVF of the LCVM with the doped ions can significantly exceed that of the fundamental mode if the proposed fiber design is applied. In addition, an RDCF of the proposed fiber design can also operate in a regime containing no higher-order modes besides the LCVM, so that it can selectively and efficiently generate the LCVM without being disrupted by the parasitic lasing of the higher-order modes. We highlight that an optimized RDCF can lead to a >30 % higher OVF ratio than a SICF having the same doped area. The proposed model is expected to be useful for enhancing the efficiency of generating CVBs in an all-fiber format.

• Smart Structures and Systems
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• 제17권2호
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• pp.313-325
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• 2016

The paper provides a comprehensive procedure for the mechanical and magnetic design of Langevin transducer based on giant magnetostrictive material. The the transducer is designed to work at its second mode of vibration, having high mechanical quality factor and low damping coefficient. The design procedure is based on an analytical model and it is verified by finite-element analysis. Experimental tests based on impedance response analysis in first and second modes are carried out on the prototype. Results confirm the appropriate design of this transducer, demonstrating the highest mechanical quality factor between the resonant transducers in the literature.

• 한국음향학회지
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• 제38권3호
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• pp.340-343
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• 2019

본 논문은 동력차에서 견인전동기 기진 주파수와 견인전동기 강체 모드 공진 문제로 인해 발생할 수 있는 현상에 대해 소개하고, 이를 제어하는데 효과적인 설계인자를 해석적으로 검토해보았다. 회전 속도가 변하는 회전기기의 경우, 공진 문제를 해결하기 위해서는 공진주파수 대역을 상용 운전 범위 바깥으로 이동시키거나 동강성을 크게 하는 등의 방법을 통하여 공진 응답이 낮아지도록 하는 방안이 있다. 견인전동기의 운전 범위는 일반적으로 0 r/min ~ 4800 r/min으로 대차모드가 이 운전 영역대를 벗어나게 설계하는 것은 현실적으로 불가능 하다. 따라서 공진 응답에 영향을 주는 설계 인자를 찾아 이를 적절하게 조정하여야 한다. 유한요소 해석 검토 결과, 견인전동기 강체모드 공진 응답에 영향을 주는 설계인자는 트랜섬파이프 간격으로 간격이 지나치게 넓게 설계될 경우 견인전동기 기진력과 강체 모드 간 공진 시 과도한 진동이 발생될 수 있음을 파악하였다.