• Journal of Power Electronics
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• 제14권5호
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• pp.1028-1037
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• 2014

To optimize controller design and improve static and dynamic performances of three-phase four-leg inverter systems, a compound control method that combines state feedback and quasi-sliding mode variable structure control is proposed. The linear coordinate change matrix and the state variable feedback equations are derived based on the mathematical model of three-phase four-leg inverters. Based on system relative degrees, sliding surfaces and quasi-sliding mode controllers are designed for converted linear systems. This control method exhibits the advantages of both state feedback and sliding mode control. The proposed controllers provide flexible dynamic control response and excellent stable control performance with chattering suppression. The feasibility of the proposed strategy is verified by conducting simulations and experiments.

• 전력전자학회논문지
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• 제26권5호
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• pp.372-375
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• 2021

A three-leg inverter-type isolated DC-DC Converter that can use 220 and 440 V grid input voltages is introduced. The secondary circuit structure of the proposed topology is center-tap, which is the same as the conventional phase-shifted full-bridge converter. However, the primary circuit structure is composed of a three-leg inverter structure and a transformer, in which two primary windings are connected in series. The proposed circuit structure has a wider input voltage range than the conventional phase-shifted full-bridge converter, and the circulating-current on the primary-side is reduced. In addition, the voltage stress at the secondary rectifier is greatly improved, and high efficiency can be achieved at a high input voltage by removing the snubber circuit added to the conventional converter. Prototype converters with input DC of 311 V, output of 622 V, and 50 V and 6 kW class specifications were designed and manufactured to verify the validity of the proposed topology; the experimental results are presented.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 2001년도 추계학술대회 학술발표 논문집
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• pp.125-128
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• 2001

This paper explains the walking robot with 4 legs. One leg is composed of 4 dc server motors and have 4 d.o.f. This walking robot has simple structure using the principle of lever. The structure of robot models the 4 legs animal such as dog. The walking patterns is various and complex. With Inspecting the walking dogs, the walking motions implemented by patterns. The center of mass is important of this type robot. The significant issue of walking is weight. As the weight is lighter, so the robot well walks. The method of walking is patterns.

• 한국전문물리치료학회지
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• 제18권2호
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• pp.60-66
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• 2011

Foot posture is important in the development of the musculoskeletal structure in the lower limbs because it can change the mechanical alignment. Although foot orthotics are widely used for the correction of malalignments in the lower extremities, the biomechanical effects of wedges have not yet been cleared. The aim of this study was to investigate whether medial wedges affect the electromyographic (EMG) activity of the knee and hip joints in healthy adults that are performing one leg standing. Seventeen healthy volunteers performed the one leg standing under two foot conditions: A level surface, and a $15^{\circ}$ medial wedge. The subjects' EMG data for the gluteus maximus (Gmax), gluteus medius (Gmed), tensor fasciae latae (TFL), biceps femoris (BF), vastus lateralis (VL), and vastus medialis oblique (VMO) were recorded, along with the surface EMG, and all were analyzed. The EMG activity of the Gmed and TFL had significantly decreased under the medial wedge condition during one leg standing. Further study is needed in order to investigate whether medial wedges influence the EMG activity and kinematic data of the knee and hip joints as well as the ankle joints in adults with flexible flatfoot, while they are performing one leg standing.

• 한국전기전자재료학회논문지
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• 제30권2호
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• pp.106-110
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• 2017

This paper compared current limiting characteristics of superconducting fault current limiter (SFCL) using E-I core due to the location of windings. Since E-I core has three legs and two magnetic paths, the current limiting characteristics of SFCL were expected to be affected by the installation location of windings, either center leg or right/left leg. To analyze its characteristics, the electrical equivalent circuit of the SFCL were derived and the electromagnetic analysis for the SFCL with the designed structure were performed. From the short-circuit tests, the hysteresis curve and the voltage-current trajectory of the SFCL due to the installation location of windings were extracted and compared each other. The SFCL with windings in the center leg of E-I core was shown to be larger magnetizing inductance compared to the one with windings in the right or left leg of E-I, which was analyzed from the hysteresis curve. In addition, larger decreased fault current right after the fault occurrence in the SFCL with windings in the center leg of E-I core was confirmed than the SFCL with windings in the right or left leg of E-I.

• Ocean Systems Engineering
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• 제4권4호
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• pp.327-342
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• 2014

The tension leg platform (TLP) is one of the compliant structures which are generally used for deep water oil exploration. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to the vertical degrees of freedom, it is stiff and resembles a fixed structure and is not allowed to float freely. In the current study, a numerical study for square TLP using modified Morison equation was carried out in the time domain with water particle kinematics using Airy's linear wave theory to investigate the effect of changing the tether tension force on the stiffness matrix of TLP's, the dynamic behavior of TLP's; and on the fatigue stresses in the cables. The effect was investigated for different parameters of the hydrodynamic forces such as wave periods, and wave heights. The numerical study takes into consideration the effect of coupling between various degrees of freedom. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables. Nonlinear equation was solved using Newmark's beta integration method. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e., 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether tension force, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations that is significantly dependent on wave height, and that special attention should be given to tethers fatigue because of their high tensile static and dynamic stress.

• 센서학회지
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• 제8권5호
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• pp.368-376
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• 1999

본 논문에서는 머리빗형 액튜에이터의 제작 공정 중에서 RIE 식각 공정시 발생하는 식각의 비등방도의 변화에 의해서 머리빗형 액튜에이터의 스프링 상수, 공진 주파수, 정전 구동력 과리고 진동자 변위 등에서 발생하는 동작 특성이 설계 값으로부터 변화되는 것을 예측하였다. 이를 위해 $6\;{\mu}m$ 두께의 폴리실리콘에 대한 RIE 식각 실험을 수행하여 RF power, $Cl_2$ 유량 그리고 챔버내 압력에 따른 비등방도를 측정하였다. 실험 결과에서 RF Power, $Cl_2$ 유량, 그리고 챔버내 압력이 증가할수록 비등방도 감소하였다. 이러한 비등방도 감소에 따른 머리빗형 구조물의 동작 특성을 세 가지 다른 지지빔의 경우에 대해 예측하였는데 세 가지는 fixed-fixed, crab-leg, 그리고 double crab-leg 구조이다. 비등방도가 감소함에 따라 즉, 지지빔의 단면이 직사각형이 아니고 사다리꼴이 되면서, 머리빗형 액튜에이더의 스프링 상수, 공진 주파수, 그리고 정전 구동력은 감소하였지만 질량체의 변위는 증가하였다. 그리고 세 가지 구조물 중에서 double crab-leg 지지빔을 갖는 머리빗형 액튜에이터의 특성이 비등방도에 의해 가장 큰 영향을 받는 것으로 나타났다.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.106-111
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• 2017

본 연구에서는 해양구조물의 상부(top side) 구조물을 설치할 때 필요한 장치인 LMU(Leg Mating Unit)의 강성을 구조해석을 통하여 검토하였다. 이것은 구조물의 지지 점에 장착되어 설치 시 충격을 흡수하고 안정적으로 구조물을 지지하는 데 사용된다. LMU는 가운데가 비어있는 원통형 구조로서 수직 하중을 지지하기 위해서 일래스토머릭 베어링(Elastomeric Bearing, 이하 EB)과 철판을 여러 층으로 적층한다. EB의 강성은 기본적으로 베어링의 크기에 영향을 받지만, 동일한 크기에서도 내부 보강판의 적층 수에 따라 강성이 변하게 된다. 일반적으로 보강판과 압축 강성 사이의 관계를 분석하여 적합한 설계를 한다. EB의 강성은 변위를 제어하면서 반력을 산출하는 방식으로 분석을 한다. 먼저 보강판의 크기와 압축 강성 관계를 검토하고, 보강판의 적층 수와 압축 강성 관계를 검토한다. LMU는 장착되는 지점마다 다른 하중이 요구된다. 해석을 통해 각 지점에서 동일한 변형이 발생하도록 압축 강성을 다르게 설계하는 것이 목표이다. 본 연구의 유한요소해석을 위하여 상용 프로그램인 ANSYS를 이용하였다.

• 한국축산식품학회지
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• 제32권5호
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• pp.578-583
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• 2012

The purpose of this study was to evaluate the ultrastructural and shear force changes of duck breast and leg meat during aging at $0^{\circ}C$. Pekin ducks (45 d old) purchased from Greemud Co. were used for this experiment, and were stored at $0^{\circ}C$ for 7 d in order to determine the changes of the meat structure using transmission electron microscopy (TEM) and shear force. At day 0, A-band, I-band, M-line and Z-line of sarcomeres were seen clearly, but sarcomeres started to lose structure and become extended in length from day 2. With extended aging periods, myofibrils were destroyed and symptoms of aging became more obvious. In the duck breast meat, some myofibrils were also destroyed at the Z-line, but were mainly destroyed at the M-line. The change in structure of duck leg meat over time was similar to that of breast meat. After five days and seven days of aging, mitochondria size and quantity were determined to be increased between the myofibrils. Shear force was decreased over time. From this study, aging at $0^{\circ}C$ was found to negatively influence the ultrastructure and shear force of duck meat.

• Journal of Welding and Joining
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• 제16권5호
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• pp.134-141
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• 1998

In this study, a fillet size for bending fatigue strength of one side fillet welded T-joint, used in box type girder and other welding structure, was investigated by bending fatigue test with or without edge preparation and burn through, with variation of joint shape. As a result, the following conclusions were obtained. (1) In one side fillet welded T-joint, the larger the leg length, the greater the bending fatigue strength. The increase in bending fatigue strength. (2) One side filet welded T-joint with edge preparation showed higher bending fatigue strength than that with twofold-large leg length and without edge preparation. (3) In one side fillet welded T-joint without edge preparation, both manual welding and automatic welding were carried out with same condition. In this case, automatic welding shoed deeper penetration and more increased horizontal leg length than manual welding, so that automatic welding offers grater bending fatigue strength. (4) For one side fillet welded T-joint without edge preparation, the ratio(h/t) of the leg length (h) and the main plate thickness (t) in which toe crack can occur was 1.2 over. (5) In one side fillet welded T-joint with edge preparation, the burn through led to reduced bending fatigue strength. However, this bending fatigue strength was higher than that of one side fillet welded T-joint without edge preparation and with a larger leg length.