• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.2
• /
• pp.262-266
• /
• 2010

During the restoration process of primary restorative transmission system, the over voltage may happen due to nonlinear interaction between the unloaded transformer and the transmission system. This over voltage is caused by harmonic resonance and can be prevented by damping loads that are connected before restoration process of primary restorative transmission system. But it is very difficult to predict the occurrence possibility of the harmonic resonance previously. This paper analyzes the relationship between the harmonic resonance and the amount of damping loads to prevent the harmonic resonance. This paper calculates the minimum amount of damping loads to prevent harmonic resonance while changing the length of primary restorative transmission line. And this paper confirmed that the amount of damping loads is not proportional to length of transmission line. The result of this paper will be used as important experiment data to predict the occurrence possibility of harmonic resonance previously.

• Computers and Concrete
• /
• v.32 no.6
• /
• pp.543-551
• /
• 2023

In this article, thermal post-buckling and primary resonance of the porous functionally graded material (FGM) beams in thermal environment considering the geometric imperfection are studied, the material properties of FGM beams are assumed to vary along the thickness of the beam, meanwhile, the porosity volume fraction, geometric imperfection, temperature, and the elastic foundation are considered, using the Euler-Lagrange equation, the nonlinear vibration equations are derived, after the dimensionless processing, the dimensionless equations of motion can be obtained. Then, the two-step perturbation method is applied to solve the vibration problems, the resonance and thermal post-buckling response relations are obtained. Finally, the functionally graded index, the porosity volume fraction, temperature, geometric imperfection, and the elastic foundation on the resonance behaviors of the FGM beams are presented. It can be found that these parameters can influence the thermal post-buckling and primary resonance problems.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.55 no.5
• /
• pp.191-194
• /
• 2006

Power system restoration following a wide area or complete blackout starts with energizing primary restorative transmission systems. During this primary restoration process, unexpected over-voltage may happen due to nonlinear interaction between the unloaded transformer and the transmission system. This is known as the harmonic resonance phenomenon that may cause burning out of transformer or other devices. Since the harmonic resonance originates from the nonlinear characteristics, it is very difficult to predict the occurrence of this phenomenon. This paper reports the analyses of the harmonic resonance occurred in domestic power system. Various analyses and results of the harmonic over-voltage is presented based on the PSCAD/EMTDC simulations.

• Structural Engineering and Mechanics
• /
• v.61 no.4
• /
• pp.497-510
• /
• 2017

A framed structure may be composed of two sub-structures, which are linked by a hinged joint. One sub-structure is the primary system and the other is the secondary system. The primary system, which is subjected to the periodic external load, can give rise to an auto-parametric resonance of the second system. Considering the geometric-stiffness effect produced by the axially internal force, the element equation of motion is derived by the extended Hamilton's principle. The element equations are then assembled into the global non-homogeneous Mathieu-Hill equations. The Newmark's method is introduced to solve the time-history responses of the non-homogeneous Mathieu-Hill equations. The energy-growth exponent/coefficient (EGE/EGC) and a finite-time Lyapunov exponent (FLE) are proposed for determining the auto-parametric instability boundaries of the structural system. The auto-parametric instabilities are numerically analyzed for the two frames. The influence of relative stiffness between the primary and secondary systems on the auto-parametric instability boundaries is investigated. A phenomenon of the "auto-parametric internal resonance" (the auto-parametric resonance of the second system induced by a normal resonance of the primary system) is predicted through the two numerical examples. The risk of auto-parametric internal resonance is emphasized. An auto-parametric resonance experiment of a ${\Gamma}$-shaped frame is conducted for verifying the theoretical predictions and present calculation method.

• Proceedings of the KIEE Conference
• /
• 2005.07a
• /
• pp.220-222
• /
• 2005

Power system restoration following a wide area or complete blackout starts with energizing primary restorative transmission systems. During this primary restoration process, unexpected over-voltage may happen due to nonlinear interaction between the unloaded transformer and the transmission system. This is known as the harmonic resonance phenomenon that may cause burning out of transformer or other devices. Since the harmonic resonance originates from the nonlinear characteristics, it is very difficult to predict the occurrence of this phenomenon. This paper reports the possible existence of the harmonic resonance in Korean power system. Analysis of the harmonic over-voltage is presented based on the various simulations using PSCAD/EMTDC.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.54 no.4
• /
• pp.172-176
• /
• 2005

Power system restoration following a massive or complete blackout starts with energizing of primary restorative transmission lines. During this primary restoration, inexpected overvoltage may happen due to nonlinear interaction between the unloaded transformer and the transmission system. This is known as the harmonic resonance phenomenon that may cause burning out of transformer or other devices. By now the harmonic resonance is reported in the extra high voltage system. This paper reports the detection of the resonance in Korean power system. Basic analysis and simulation of the harmonic overvoltage is presented using EMTDC.

• Journal of Aerospace System Engineering
• /
• v.13 no.5
• /
• pp.9-15
• /
• 2019

In this paper, dynamic analysis of a nonlinear active vibration absorber is conducted with a time delay acceleration feedback to suppress the vibration of a nonlinear single degree of freedom primary system. The primary system consisting of linear and nonlinear cubic springs, mass, and damper is subjected to the multi-harmonic hard excitation with a parametric excitation. It is proposed to reduce the vibration of the primary system and the absorber by using a lead zirconate titanate (PZT) stack actuator in series with a spring in the absorber which configures as an active vibration absorber. The method of multiple scales (MMS) is used to obtain the approximate solution of the system under the internal resonance, subharmonic, superharmonic, and principal parametric resonance conditions simultaneously. Frequency and time responses of the system are investigated considering a delay in the feedback for the various parameters of the absorber configuration and controlling force.

• Steel and Composite Structures
• /
• v.48 no.3
• /
• pp.335-351
• /
• 2023

This research studies the primary resonance and nonlinear vibratory responses of multilayer functionally graded shallow (MFGS) shells under external excitations. The shells considered with functionally graded porous (FGP) core and resting on two types of nonlinear viscoelastic foundations (NVEF) governed by either a linear model with two parameters of Winkler and Pasternak foundations or a nonlinear model of hardening/softening cubic stiffness augmented by a Kelvin-Voigt viscoelastic model. The shells considered have three layers, sandwiched by functionally graded (FG), FGP, and FG materials. To investigate the influence of various porosity distributions, two types of FGP middle layer cores are considered. With the first-order shear deformation theory (FSDT), Hooke's law, and von-Kármán equation, the stress-strain relations for the MFGS shells with FGP core are developed. The governing equations of the shells are consequently derived. For the sake of higher accuracy and reliability, the P-T method is implemented in numerically analyzing the vibration, and the method of multiple scales (MMS) as one of the perturbation methods is used to investigate the primary resonance. The results of the present research are verified with the results available in the literature. The analytical results are compared with the P-T method. The influences of material, geometry, and nonlinear viscoelastic foundation parameters on the responses of the shells are illustrated.

• Investigative Magnetic Resonance Imaging
• /
• v.22 no.4
• /
• pp.240-244
• /
• 2018

Primary extranodal bone lymphoma involving the peripheral extremities is extremely rare. Here, we report a definitive case of diffuse large B-cell lymphoma involving the phalangeal bone of the 3rd finger. Systemic evaluation revealed the lesion as the only site of lymphoma involvement.

• Investigative Magnetic Resonance Imaging
• /
• v.21 no.4
• /
• pp.252-258
• /
• 2017

Primary mesenteric liposarcoma is rare. It is difficult to make an accurate preoperative diagnosis of the myxoid type of liposarcoma by using imaging such as ultrasound or computed tomography (CT) due to the very small amount of fat that is located in the tumor. We report a case of primary myxoid liposarcoma of the mesentery which was difficult to differentiate from other solid mesenteric tumors with a myxoid component such as low grade fibromyxoid sarcoma, myxoid leiomyosarcoma or myxoma. Use of chemical shift magnetic resonance (MR) imaging to detect small fat components and its cystic appearance with solid components on the MR images can be useful to differentiate myxoid liposarcoma from the other mesenteric tumors with a myxoid component.