• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 추계학술대회논문집
• /
• pp.255-261
• /
• 2002

A four-degree of freedom model is suggested to understand the basic dynamical behaviors of the normal interaction between two masses of the friction induced normal vibration system. The two masses may be considered as the pad and the disk of the brake. The phase space analysis is performed to understand complicated in-plane dynamics of the non-linear model. Attractors in the phase space are examined for various conditions of the parameters. In certain conditions, the attractor becomes a limit cycle showing the stick-slip phenomena. In this paper, on the basis of the in-plane motion not only the existence of the limit cycle but also the size of the limit cycle is examined o demonstrate the non-linear dynamics that leads the unstable state and then the normal vibration is investigated as the state of the in-plane motion For only one case of the system frequency(two masses with same natural frequencies), the propensity of the normal vibration is discussed in detail. The results show an important fact that it may be not effective when too much damping is present in the only one part of the masses.

• Journal of Electrical Engineering and Technology
• /
• 제13권1호
• /
• pp.20-29
• /
• 2018

The dynamic characteristics of power systems become more and more complex because of the integration of large-scale wind power, which needs appropriate control strategy to guarantee stable operation. With wide area measurement system(WAMS) creating conditions for realizing realt-ime transient stability analysis, a new coordinated control strategy for power system transient stability control based on phase-plane trajectory was proposed. When the outputs of the wind farms change, the proposed control method is capable of selecting optimal generators to balance the deviation of wind power and prevent transient instability. With small disturbance on the base operating point, the coordinated sensitivity of each synchronous generator is obtained. Then the priority matrix can be formed by sorting the coordinated sensitivity in ascending order. Based on the real-time output change of wind farm, coordinated generators can be selected to accomplish the coordinated control with wind farms. The results in New England 10-genrator 39-bus system validate the effectiveness and superiority of the proposed coordinated control strategy.

• 대한기계학회논문집B
• /
• 제26권2호
• /
• pp.362-373
• /
• 2002

A stereoscopic PIV (SPIV) measurement system based on the translation configuration was developed and applied to the flow behind a forward-swept axial-fan. Measurement of three orthogonal velocity components is essential for flow analysis of three-dimensional flows such as flow around a fan or propeller. In this study, the translation configuration was adopted to calculate the out-of-plane velocity component from 2-D PIV data obtained from two CCD cameras. The error caused by the out-of-plane motion was estimated by direct comparison of the 2-D PIV and 3-D SPIV results that measured from the particle images captured simultaneously. The comparison shows that the error ratio is relatively high in the region of higher out-of-plane motion near the axial fan blade. The turbulence intensity measured by the 2-D PIV method is bigger by about 5.8% in maximum compared with that of the 3-D SPIV method. The phase-averaged velocity field results show that the wake behind an axial fan has a periodic flow structure with respect to the blade phase and the characteristic flow structure is shifted downstream in the next phase.

• 대한전기학회논문지
• /
• 제43권7호
• /
• pp.1075-1083
• /
• 1994

In this paper, a study on the improvement of the IM speed response against load torque variation is presented. A VSCS(Variable Structure Control System) is proposed which gives the desired robustness against load torque variation using a new kind of time-varing switching plane. In order to eliminate the reaching phase of the states from one switching plane to another during variation, the switching plane is varied continuously. To verify the high dynamic performance of the proposed VSCS, simulation and experimental results are presented.

• Structural Engineering and Mechanics
• /
• 제59권3호
• /
• pp.403-430
• /
• 2016

This paper studies the dynamics of the lineal-located time-harmonic moving-with-constant-velocity load which acts on the hydro-elastic system consisting of the elastic plate, compressible viscous fluid - strip and rigid wall. The plane-strain state in the plate is considered and its motion is described by employing the exact equations of elastodynamics but the plane-parallel flow of the fluid is described by the linearized Navier-Stokes equations. It is assumed that the velocity and force vectors of the constituents are continuous on the contact plane between the plate and fluid, and impermeability conditions on the rigid wall are satisfied. Numerical results on the velocity and stress distributions on the interface plane are presented and discussed and the focus is on the influence of the effect caused by the interaction between oscillation and moving of the external load. During these discussions, the corresponding earlier results by the authors are used which were obtained in the cases where, on the system under consideration, only the oscillating or moving load acts. In particular, it is established that the magnitude of the aforementioned interaction depends significantly on the vibration phase of the system.

• 대한조선학회논문집
• /
• 제41권4호
• /
• pp.30-37
• /
• 2004

Flow characteristics of the inflow ahead of a rotating propeller attached to a container ship model were investigated using a two-frame PIV (Particle Image Velocimetry) technique. Ensemble-averaged mean velocity fields were measured at four different blade phases. The mean velocity fields show the acceleration of inflow due to the rotating propeller and the velocity deficit in the near-wake region. The axial velocity distribution of inflow in the upper plane of propeller is quite different from that in the lower plane due to the thick hull boundary layer. The propeller inflow also shows asymmetric axial velocity distribution in the port and starboard side. As the inflow moves toward the propeller, the effect of phase angle variation of propeller blade on the inflow becomes dominant. In the upper plane above the propeller axis the inflow has very low axial velocity and large turbulent kinetic energy, compared with the lower plane. The boundary layer developed along the bottom surface of stern hull forms a strong shear layer affecting vortex structure of the propeller near-wake.

• Steel and Composite Structures
• /
• 제22권3호
• /
• pp.567-587
• /
• 2016

The present investigation is to study the plane wave propagation and reflection of plane waves in a homogeneous transversely isotropic magnetothermoelastic medium with two temperature and rotation in the context of GN Type-II and Type-III (1993) theory of thermoelasticity. It is found that, for two dimensional assumed model, there exist three types of coupled longitudinal waves, namely quasi-longitudinal wave (QL), quasi-transverse wave (QTS) and quasi-thermal waves (QT). The different characteristics of waves like phase velocity, attenuation coefficients, specific loss and penetration depth are computed numerically and depicted graphically. The phenomenon of reflection coefficients due to quasi-waves at a plane stress free with thermally insulated boundary is investigated. The ratios of the linear algebraic equations. These amplitude ratios are used further to calculate the shares of different scattered waves in the energy of incident wave. The modulus of the amplitude and energy ratios with the angle of incidence are computed for a particular numerical model. The conservation of energy at the free surface is verified. The effect of energy dissipation and two temperatures on the energy ratios are depicted graphically and discussed. Some special cases of interest are also discussed.

• 한국광학회지
• /
• 제16권3호
• /
• pp.239-247
• /
• 2005

본 연구에서는 물체의 내부 결함 측정을 위해서 레이저 스페클에 바탕을 둔 dual-beam shearography 기술을 이용하였다. 층 밀림을 만들기 위해서는 여러 가지 간섭계 중에서 마이켈슨 층 밀림 간섭계를 사용하였다. 열전도도가 낮은 아크릴 판 내부에 인위적인 결함을 만들어서 시료로 사용하였다. 시료에 레이저 beam을 조사하여 산란된 빛을 마이켈슨 층 밀림 간섭계를 통하여 스페클 간섭무의를 얻었으며, 위상이동기술을 통하여 위상도를 얻었다. 단일 beam을 시료에 조사할 경우, 물체의 변형의 in-plane과 out-of-plane 성분이 혼합된 상태로 측정되기 때문에 결함에 대한 정확한 분석이 불가능하다. 따라서 두 성분을 분리하기 위해서 dual-beam shearography 기술을 도입하였다. 내부 결함이 있는 시료에 이중 beam을 조사하여 변형 전의 간섭 스페클을 얻고, 약간의 전기 열을 가하여 미세한 변형을 가한 후의 간섭스페클을 얻은 후 의 위상도를 얻은 후 LS filtering과 unwrapping 처리를 통하여 내부 결함 부위를 쉽게 알아볼 수 있도록 하였을 뿐 아니라, 외력에 의한 물체의 미세 변형에 따른 결함 부위에서의 in-plane과 out-of-plane 변형성분의 위상도와 대략적인 변형 정도를 알아낼 수 있었다. 전기 열에 의한 내부결함이 있는 아크릴 판의 변형은 주로 z 방향(out-of-plane)으로 일어났으며 이것은 낮은 열전도도 때문이라는 예측과 잘 일치하였다.

• 대한전자공학회논문지
• /
• 제15권6호
• /
• pp.79-86
• /
• 1978

위상이 2진적으로 변하고 주파수가 계단적으로 변하는 연속펄스 열로 된 FM 신호를 레이다 신호로 전용할 때의 특성을 고찰하였다. 이 목적을 위하여 우선 이런 종류의 신호에 대한 스퍽트럼 및 애요함수에 대한 일반적인 표시식을 구하였으며 다음에 여러가지 2진위상 코딩에 대하여 그 스펙트림과 애요함수의 크기를 콤퓨터에 의하여 프롯터로 그렸다. 이 결과로 부터 위상이 교대로 변하는 경우가 다른 코딩 방식에 비하여 가장 양호한 시간분해능을 가진다는 것과 또 이 경우의 천체함수는 시간-속도의 전평면상에서 다수의 스파이크를 가진다는 것을 알았다.

• 한국정밀공학회지
• /
• 제15권12호
• /
• pp.113-119
• /
• 1998

Recently Electronic Speckle Pattern Interferometry(ESPI) has been studied because it has the advantages to be able to measure the whole-field surface deformations of engineering components and materials in industrial areas with noncontact. The speckle patterns to be formed with interference phenomena of scattering light from rough surfaces illuminated by laser light have phase informations of surface deformations. In this study we used this interference phenomena and the phase shifting method to measure the inplane deformations, together with the use of digital image equipment to process the informations contained in the speckle pattern and to display consequent interferograms on TV monitor. FEA was performed before experiments and we obtained good agreement between the experimental results and FEA.