• 대한기계학회논문집A
• /
• 제27권12호
• /
• pp.2011-2018
• /
• 2003

To analyze the bending collapse behavior of an aluminum square tube beam under a bending load, a finite element simulation for the four-point bending test has been performed. Using an aluminum tube beam specimen partly inserted with two steel bars, the local buckling deformation near the center of the tube beam was induced. The maximum bending load and the bending collapse behavior obtained from the numerical simulation were in good agreement with experimental results. Using a combination of the four-point bending test and its finite element simulation, analysis of the local buckling and the accompanied bending collapse behavior of aluminum tube beam could be quantitative accomplished.

• Journal of Power Electronics
• /
• 제17권5호
• /
• pp.1268-1277
• /
• 2017

Three-phase pulse width modulation (PWM) rectifiers are usually designed under the assumption of ideal ac power supply and input inductance. However, non-ideal circuit parameters may lead to a voltage collapse of PWM rectifiers. This paper investigates the mechanism of voltage collapse in three-phase PWM rectifiers. An analytical stability boundary expression is derived by analyzing the equilibrium point of the averaging state space model, which can not only accurately locate the voltage collapse boundary in the circuit parameter domain, but also reveal the essential characteristic of the voltage collapse. Results are obtained and compared with those of the trial-error method and the Jacobian method. Based on the analysis results, the system parameters can be divided into two categories. One of these categories affects the critical point, and other affects only the instability process. Furthermore, an effective control strategy is proposed to prevent a vulnerable system from being driven into the instability region. The analysis results are verified by the experiments.

• 대한전기학회논문지:전력기술부문A
• /
• 제50권10호
• /
• pp.472-479
• /
• 2001

In order to prevent voltage collapse. this paper introduces the idea of the intelligent system and operating polices for a power system, then presents the results of voltage stability studies for that power system. The intelligent system includes a dedicated computer doing calculation and evaluation jobs and several intelligent relays serving as last guards to carry out the pre-set remedies. In the intelligent system, P-V curves are used to determine the operating margin from the current operating point to the maximum operating point, or the nose point. This paper suggests an operating guide for voltage stability of a power system. The effectiveness of location ad amount of load shedding for the different power load models are studied.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2002년도 춘계학술대회 논문집
• /
• pp.17-20
• /
• 2002

Recently tube hydroforming technology has been one of the most important technology in automotive industry in the point of saving weight and high quality for collision accidents. In this paper, experimental studies for axial compression tests of hydroformed tubes are performed to investigate the collapse absorption characteristics. The collapse absorption abilities are discussed and compared for as-received, hydroformed, and press formed tubes.

• 대한전기학회논문지:전력기술부문A
• /
• 제48권8호
• /
• pp.951-957
• /
• 1999

The saddle node bifurcation (SNB) and the distance voltage instability are valuable information in power system planning and operation. This paper presents a new efficient, robust and unified strategy to compute the SNB by the combined use of the continuation power flow (CPF), Point of Collapse (PoC) method, and the method of a pair of multiple load flow solutions (PMLFS) with Lagrange interpolation utilizing only their advantages: the approximate nose curves and critical loading are determined fast by Lagrange-interpolating two stable and two unstable solutions obtained by using the robust CPF and PMLFS; the exact SNB is computed by the quadratically converging PoC method. The proposed method has been tested on Klos-Kerner 11-bus, New England 30-bus, IEEE 118-bus and KEPCO 791-bus systems. The method is found to be so efficient that computation time for determining the SNB of the KEPCO 791-bus system is 17.82 sec by a notebook PC with 300 MHz Pentium processor.

• Journal of Electrical Engineering and Technology
• /
• 제11권1호
• /
• pp.1-8
• /
• 2016

It is well known that the behavior of PV curves is similar to a quadratic function. This is used in some papers to approximate PV curves and calculate the maximum-loading point by minimum number of power flow runs. This paper also based on quadratic approximation of the PV curves is aimed at completing previous works so that the computational efforts are reduced and the accuracy is maintained. To do this, an iterative method based on a quadratic function with two constant coefficients, instead of the three ones, is used. This simplifies the calculation of the quadratic function. In each iteration, to prevent the calculations from diverging, the equations are solved on the assumption that voltage magnitude at a selected load bus is known and the loading factor is unknown instead. The voltage magnitude except in the first iteration is selected equal to the one at the nose point of the latest approximated PV curve. A method is presented to put the mentioned voltage in the first iteration as close as possible to the collapse point voltage. This reduces the number of iterations needed to determine the maximum-loading point. This method is tested on four IEEE test systems.

• 한국전산구조공학회논문집
• /
• 제20권4호
• /
• pp.435-442
• /
• 2007

1968년 영국의 Ronan Point 아파트에서 발생한 연쇄붕괴 이후 이에 대한 연구가 간헐적으로 진행되어 왔으며, 최근 미국의 World Trade Center 붕괴 후 연쇄붕괴에 대한 연구가 다시 활발히 진행되고 있다. 미국에서는 기존의 연구결과를 바탕으로 2003년 GSA 및 2005년 DoD에서 연쇄붕괴에 대한 설계 및 해석 지침을 제시하였다. 본 연구에서는 이러한 지침서에서 제시하고 있는 선형정적해석법과, 선형동적해석법을 사용하여 국내 설계기준에 의해 설계된 철골 모멘트저항골조에 대한 붕괴저항 성능을 조사하였다. 해석결과에 따르면 GSA 기준을 적용할 경우 횡력을 고려하지 않은 수직저항시스템은 연쇄 붕괴에 취약한 것으로 나타났으나, 지진력을 고려하여 설계된 수평저항시스템은 연쇄붕괴에 대해 안전한 결과를 얻었다. 하지만 DoD 기준에 따르면 두 시스템 모두 연쇄붕괴에 취약한 것으로 나타났다.

• Earthquakes and Structures
• /
• 제3권3_4호
• /
• pp.473-494
• /
• 2012

The capacity of pipelines to resist collapse under external pressure and bending moment is a major aspect of deepwater pipeline design. Existing design codes present interaction equations that quantify pipeline capacities under such loadings, although reasonably accurate, are based on empirical data fitting of the bending strain, and assumed simplistic interaction with external pressure collapse. The rational model for collapse of deepwater pipelines, which are relatively thick with a diameter-to-thickness ratio less than 40, provides a unique theoretical basis since it is derived from first principles such as force equilibrium and compatibility equations. This paper presents the rational model methodology and compares predicted results and recently published full scale experimental data on the subject. Predictive capabilities of the rational model are shown to be excellent. The methodology is extended for the problem of pipeline collapse under point load, longitudinal bending and external pressure. Due to its rational derivation and excellent prediction capabilities, it is recommended that design codes adopt the rational model methodology.

• 대한전기학회논문지
• /
• 제43권6호
• /
• pp.869-876
• /
• 1994

This paper presents an efficient method to calculate voltage collapse point and to avoid voltage instability. To evaluate voltage stability in power systems, it is necessary to get critical loading points. For this purpose, this paper uses linear programming to calculate efficiently voltage collapse point. Also, if index value becomes larger than given threshold value, voltage stability is improved by compensation of reactive power at selected bus. This algorithm is verified by simulation on the IEEE 14-bus sample system.

• International Journal of Fluid Machinery and Systems
• /
• 제2권2호
• /
• pp.165-171
• /
• 2009

We developed a 'multi-point vibration acceleration method' for accurately predicting the cavitation intensity in pumps. Pressure wave generated by cavitation bubble collapse propagates and causes pump vibration. We measured vibration accelerations at several points on a casing, suction and discharge pipes of centrifugal and mixed-flow pumps. The measured vibration accelerations scattered because the pressure wave damped differently between the bubble collapse location and each sensor. In a conventional method, experimental constants are proposed without evaluating pressure propagation paths, then, the scattered vibration accelerations cause the inaccurate cavitation intensity. In our method, we formulated damping rate, transmittance of the pressure wave, and energy conversion from the pressure wave to the vibration along assumed pressure propagation paths. In the formulation, we theoretically defined a 'pressure propagation coefficient,' which is a correlation coefficient between the vibration acceleration and the bubble collapse pressure. With the pressure propagation coefficient, we can predict the cavitation intensity without experimental constants as proposed in a conventional method. The prediction accuracy of cavitation intensity is improved based on a statistical analysis of the multi-point vibration accelerations. The predicted cavitation intensity was verified with the plastic deformation rate of an aluminum sheet in the cavitation erosion area of the impeller blade. The cavitation intensities were proportional to the measured plastic deformation rates for three kinds of pumps. This suggests that our method is effective for estimating the cavitation intensity in pumps. We can make a cavitation intensity map by conducting this method and varying the flow rate and the net positive suction head (NPSH). The map is useful for avoiding the operating conditions having high risk of cavitation erosion.