• 한국공작기계학회논문집
• /
• 제11권3호
• /
• pp.65-71
• /
• 2002

Friction welding has may merits such as energy efficiency, simple processing, etc. but it is difficult to obtain good welding at the welded interfaces and heat affected zone. It is discovered that stress singularity exists at the interferes and heat affected zone. The computer program based on boundary element method is utilized in this study. A mathematical model is implemented based on results from several experiments performed at and around the welded interfaces and heat affected zone of disimilar metals under static and dynamic loadings. This stay is to investigate the characteristics of the deformation and fracture behavior around interfaces for friction welded materials under static tensile load. Also, the stress distribution at the tip of crack is analyzed by using BU based on Kelvin's solution of 2-dimensional binding zone. The results of BEM are identical with those in case of considering interfaces of both heat affected zone. Also, stress singularity at the tip of interfaces appears when the elastic modulus ratio is 1.07.

• Structural Engineering and Mechanics
• /
• 제75권2호
• /
• pp.211-227
• /
• 2020

The contribution of infill wall is generally not considered in the structural analysis of reinforced concrete (RC) structures due to the lack of knowledge of the complex behavior of the infilled frame of RC structures. However, one of the significant factors affecting structural behavior and earthquake performance of RC structures is the infill wall. Considering structural and architectural features of RC structures, any infill wall may have openings with different amounts and aspect ratios. In the present study, the influence of infill walls with different opening rates on the structural behaviors and earthquake performance of existing RC structures were evaluated. Therefore, the change in the opening ratio in the infill wall has been investigated for monitoring the change in structural behavior and performance of the RC structures. The earthquake performance levels of existing RC structures with different structural properties were determined by detecting the damage levels of load-carrying components. The results of the analyzes indicate that the infill wall can completely change the distribution of column and beam damage level. It was observed that the openings in the walls had serious impact on the parameters affecting the behavior and earthquake performance of the RC structures. The infill walls have a beneficial effect on the earthquake performance of RC structures, provided they are placed regularly and there are appropriate openings rate throughout the RC structures and they do not cause structural irregularities.

• 한국항행학회논문지
• /
• 제13권6호
• /
• pp.950-956
• /
• 2009

이동통신 수요가 폭발적으로 증가하고 있는 현재의 시장 요구 속에서 유한적인 자원인 주파수는 부족현상에 시달리고 있다. 이 문제를 해결하기 위하여 여러 각도에서 이동통신을 위한 주파수 효율성 제고를 위한 채널할당 연구가 있다. 그러나 대부분의 연구가 1:1 개별통화 위주의 이동통신에 집중되어있다. 따라서 본 논문에서는 기지국별단말의 군집성에 영향을 받는 비상재난통신을 위한 디지털 TRS 시스템 환경에서 1:N 그룹통화에 적합한 수신채널할당 기법을 제안하고 호손율 및 부하분산에서 성능개선이 있음을 보인다.

• 물과 미래
• /
• 제24권1호
• /
• pp.63-71
• /
• 1991

본 연구는 터널식 소수력 발전소의 타당성 검토 기법에 관한 것으로 개발 후보지의 유량지속곡선을 작성하기 위해서 Weibull분포의 누적밀도함수와 Thiessen법을 채택하였고, 터널식 소수력 발전소의 성능예측 모델과 건설비 산정 모델이 개발되었다. 또한 한강 수계에 산재한 8개소의 개발후보지를 선정, 실측하여 이들을 대상으로 성능 특성 및 경제적 타당성을 분석하였다. 분석 결과, 터널식 소수력 발전소의 경우 발전단가를 가장 낮게 하여 주는 최적 설계유량은 유량지속곡선상의 시간비가 20%에서 30%사이에 해당하는 유량이라는 것이 밝혀졌다. 또한 개발 후보지의 설계유량, 유효낙차, 설비용량, 년평균 가동율, 년간 전기 생산량 등과 같은 초기설계제원이 산정되었다.

• 한국해양공학회지
• /
• 제17권3호
• /
• pp.46-51
• /
• 2003

Acoustic emission (AE) signals, emanated during local failure of aluminum alloys, have been the subject of numerous investigations. It is well known that the characteristics of AE are strongly influenced by the previous thermal and mechanical treatment of the sample. Possible sources of AE during deformation have been suggested as the avalanche motion of dislocations, fracture of brittle particles, and debonding of these particles from the alloy matrix. The goal of the present study is to determine if AE occurring as the result of fatigue crack propagation could be evaluated by the joint time-frequency analysis method, short time Fourier transform (STFT), and Wigner-Ville distribution (WVD). The time-frequency analysis methods can be used to analyze non-stationary AE more effectively than conventional techniques. STFT is more effective than WVD in analyzing AE signals. Noise and frequency characteristics of crack openings and closures could be separated using STFT. The influence of various fatigue parameters on the frequency characteristics of AE signals was investigated.

• Journal of Electrical Engineering and Technology
• /
• 제13권2호
• /
• pp.752-760
• /
• 2018

In this paper, interior permanent magnet synchronous motor (IPMSM) design for sensorless drive, considering magnetic neutral point shift according to magnetic saturation, has been proposed. Sensorless control was divided into a method based on inductance and a method based on back induced voltage. Because induced voltage is very small at zero or low speed, error in rotor initial position estimation may occur. Using the ratio of saliency addresses this problem. When using high-frequency injections at low speed, the rotor's initial position is estimated at the smallest portion of the inductance. IPMSM has the minimum inductance at the d-axis. However, if magnetic saturation leads to magnetic neutral point variation, following the load current change, there is a change in the minimum point of inductance. In this case, it can lead to failure of initial rotor position estimation. As a result, it is essential that the blocking design has an inductance minimum point shift. As such, in this study, an IPMSM design method, by blocking magnetic neutral point change, has been proposed. After determining the inductance profile based on the finite element analysis (FEA), the results of proposed method were verified.

• 한국산학기술학회논문지
• /
• 제16권6호
• /
• pp.4185-4191
• /
• 2015

최근 철도의 고속화에 따라 철도수송의 안전성에 대한 요구는 증가되며, 기존 선로에 더 무거운 축중의 차량이 운행토록 요구되고 있다. 이러한 요구를 충족하기 위하여 기존 선로의 레일의 중량을 증가시키고, 장대레일화를 진행해왔다. 최근 개발된 H형 침목은 기존의 일자형 PC침목에 비해 저항 특성이 높아 궤도 강성 증대와 궤도틀림 저감을 기대할 수 있으나, H형 침목 부설에 따른 궤도 특성 변화에 대한 연구는 미흡한 실정이다. 본 논문에서는 3차원 유한요소해석을 통하여 H형 침목이 부설된 궤도의 특성을 분석하였다.

• Steel and Composite Structures
• /
• 제33권3호
• /
• pp.463-472
• /
• 2019

Initial thermo-elastic and steady state creep deformation of a rotating functionally graded simple blade is studied using first-order shear deformation theory. A variable thickness model for cantilever beam has been considered. The blade geometry and loading are defined as functions of length so that one can define his own blade profile and loading using any arbitrary function. The blade is subjected to a transverse distributed load, an inertia body force due to rotation and a distributed temperature field due to a thermal gradient between the tip and the root. All mechanical and thermal properties except Poisson's ratio are assumed to be longitudinally variable based on the volume fraction of reinforcement. The creep behaviour is modelled by Norton's law. Considering creep strains in stress strain relation, Prandtl-Reuss relations, Norton' law and effective stress relation differential equation in term of effective creep strain is established. This differential equation is solved numerically. By effective creep strain, steady state stresses and deflections are obtained. It is concluded that reinforcement particle size and form of distribution of reinforcement has significant effect on the steady state creep behavior of the blade.

• Advances in Energy Research
• /
• 제3권2호
• /
• pp.81-95
• /
• 2015

Microgrid, which can be considered as an integration of various dispersed resources (DRs), is characterized by number of DRs interfaced through the power electronics converters. The microgrid comprising these DRs is often operated in an islanded mode. To minimize the cost, reduce complexity and increase reliability, it is preferred to avoid any communication channel between them. Consequently, the droop control method is traditionally adopted to distribute active and reactive power among the DRs operating in parallel. However, the accuracy of distribution of active and reactive power among the DRs controlled by the conventional droop control approach is highly dependent on the value of line impedance, R/X i.e., resistance to reactance ratio of the line, voltage setting of inverters etc. The limitations of the conventional droop control approach are demonstrated and a modified droop control approach to reduce the effect of impedance mis-match and improve the time response is proposed. The error in reactive power sharing is minimized by inserting virtual impedance in line with the inverters to remove the mis-match in impedance. The improved time response is achieved by modifying the real-power frequency droop using arctan function. Simulations results are presented to validate the effectiveness of the control approach.

• Steel and Composite Structures
• /
• 제32권5호
• /
• pp.611-632
• /
• 2019

In this work, a four-variable refined plate model is applied to study the thermomechanical bending of two kinds of functionally graded material (FGM) sandwich plates. The sandwich core of one kind is isotropic with the FGM face sheets whereas in the second kind, the sandwich core is FGM with the isotropic and homogeneous face sheets. By considering only four unknown variables, the governing equations are written based on the principle of virtual work and then Navier method is employed to solve these equations. Deflections and stresses of two kinds of FGM sandwich structures are analyzed and discussed. The validity and efficiency of the proposed model is checked by comparing it with various available solutions in the literature. The effects of volume fraction distribution, geometric ratio and thermal load on thermomechanical bending properties of FGM sandwich plate are investigated in detail.