• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1719-1728
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• 2017

Recent concerns about environmental conditions have triggered the growing interest in using green energy resources. These sources of energy, however, bring new challenges mainly due to their uncertainty and intermittency. In order to alleviate the concerns on the penetration of intermittent energy resources, this paper investigates impacts of realizing demand-side potentials. Among different demand-side management programs, this paper considers demand response wherein consumers change their consumption pattern in response to changing prices. The research studies demand response potentials from different load sectors on generation system well-being. Consumers' sensitivity to time-varying prices is captured via self and cross elasticity coefficients. In the calculation of well-being indices, sequential Monte Carlo simulation approach is accompanied with fuzzy logic. Finally, IEEE-RTS is used as the test bed to conduct several simulations and the associated results are thoroughly discussed.

• 대한기계학회논문집A
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• 제26권12호
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• pp.2647-2655
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• 2002

This research presents an analytical model to investigate the stability due to the ball bearing waviness i n a rotating system supported by two ball bearings. The stiffness of a ball bearing changes periodically due to the waviness in the rolling elements as the rotor rotates, and it can be calculated by differentiating the nonlinear contact forces. The linearized equations of motion can be represented as a parametrically excited system in the form of Mathieu's equation, because the stiffness coefficients have time -varying components due to the waviness. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as the simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving the Hill's infinite determinant of these algebraic equations. The validity of this research is proved by comparing the stability chart with the time responses of the vibration model suggested by prior researches. This research shows that the waviness in the rolling elements of a ball bearing generates the time-varying component of the stiffness coefficient, whose frequency is called the frequency of the parametric excitation. It also shows that the instability takes place from the positions in which the ratio of the natural frequency to the frequency of the parametric excitation corresponds to i/2 (i=1,2,3..).

• 한국콘텐츠학회논문지
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• 제10권5호
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• pp.210-219
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• 2010

본 연구에서는 선택모형을 이용하여 소비자패널자료를 분석함에 있어 시간의 흐름에 따라 동적(dynamic)으로 변화하는 소비자내부의 특성 차이를 반영한 특정소비자의 종적인 변화인 소비자동태성을 분석하였다. 선택모형 내에서 소비자동태성은 효용함수에 시변계수(time-varying coefficient)를 도입함으로써 표현될 수 있다. 본 연구에서는 이를 위해 계층적모형(hierarchical model)과 상태공간모형(state-space model)에 기반하여 Random-Walk 계수를 지니는 이산프로빗모형을 개발하였고, 개발된 모형을 패널자료로부터 추정하기 위하여 Gibbs 표본법을 적용하였다. 모형추정결과 효용함수의 시변계수들에 유의한 소비자동태성이 존재함을 확인할 수 있었다. 소비자동태성이 존재할 경우 이에 효과적으로 대응하기 위해서는 동적시장세분화가 필요하다고 할 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.181-189
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• 2002

This research presents an analytical model to investigate the stability due to the ball bearing waviness in a rotating system supported by two ball bearings. The stiffness of a ball bearing changes periodically due to the waviness in the rolling elements as the rotor rotates, and it can be calculated by differentiating the nonlinear contact forces. The linearized equations of motion can be represented as a parametrically excited system in the form of Mathieu's equation, because the stiffness coefficients have time-varying components due to the waviness. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as the simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving the Hill's infinite determinant of these algebraic equations. The validity of this research is proved by comparing the stability chart with the time responses of the vibration model suggested by prior researches. This research shows that the waviness in the rolling elements of a ball bearing generates the time-varying component of the stiffness coefficient, whose frequency is called the frequency of the parametric excitation. It also shows that the instability takes place from the positions in which the ratio of the natural frequency to the frequency of the parametric excitation corresponds to i/2 (i= 1,2,3..).

• 소음진동
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• 제9권3호
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• pp.593-599
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• 1999

A rotordynamic analysis is performed with a motor-bull gear rotor system supported on two partial bearings, which is intended to drive a high-speed turbo-chiller compressor impeller shaft through its built-in pinion gear. The motor-bull gear rotor system has a rated speed of 3,600 rpm, and is modeled utilizing the finite element method for analysis. As loadings on the bearings due to the gear action are significant in the system considered, each resultant bearing load is calculated statically by considering the generalized forces of the gear action as well as the rotor itself. The two support partial bearings are designed to take their varying loads along with their varying load angles, and they are also analyzed to give their rotordynamic coefficients. Then, a complex rotordynamic analysis of the motor-bull gear rotor-bearing system is carried out to evaluate its whirl natural frequencies and mode shapes and unbalance responses under various loading conditions. Results show that the bearings and entire rotor system are well designed regradless of operating conditions, i.e., loads and operating speeds.

• Steel and Composite Structures
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• 제45권4호
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• pp.547-554
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• 2022

This paper studies the static stability of an axially graded column with the power-law gradient varying along the axial direction. For a nonhomogeneous column with one end linked to a rotational spring and loaded by a compressive force, respectively, an Euler problem is analyzed by solving a boundary value problem of an ordinary differential equation with varying coefficients. Buckling loads through the characteristic equation with the aid of the Bessel functions are exactly given. An alternative way to approximately determine buckling loads through the integral equation method is also presented. By comparing approximate buckling loads with the exact ones, the approximate solution is simple in form and enough accurate for varying power-law gradients. The influences of the gradient index and the rotational spring stiffness on the critical forces are elucidated. The critical force and mode shapes at buckling are presented in graph. The critical force given here may be used as a benchmark to check the accuracy and effectiveness of numerical solutions. The approximate solution provides a feasible approach to calculating the buckling loads and to assessing the loss of stability of columns in engineering.

• 한국강구조학회 논문집
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• 제13권5호
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• pp.547-556
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• 2001

본 연구에서는 실험을 통해 용접이음부의 형상 및 구속도의 크기 등을 변화시켜 측정한 용접 각변형량과 FEM해석을 이용한 해석결과로부터 구속계수를 유도하고 이를 고려한 등가하중을 결정하는 새로운 방법을 제시하였다. 새롭게 제시한 등가하중 결정 방법에 의한 수치해석결과는 실험결과와 잘 일치하여 그 타당성이 검증되었으며, 크기와 형상에 관계없이 대형구조물의 용접변형량을 예측하는데도 확대 적용할 수 있다. 한편 용접이음부 형상에 따른 구속에 대한 영향을 보면 맞대기용접의 경우 구속계수를 고려하지 않으면 실제 변형량보다 변형이 크게 발생하여 구속에 대한 영향을 크게 받으며 필렛용접의 경우 구속계수의 고려 유 무에 관계없이 거의 같은 변형량이 발생함으로써 구속에 대한 영향이 작음을 알 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.141-146
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• 2013

This research investigates the stability analysis for the rotating and the stationary grooved journal bearing. The dynamic coefficients of the journal bearing are calculated by using FEM and the perturbation method. When journal bearing is in whirling motion, the dynamic coefficients have time-varying components as a sine wave due to the reaction force of oil film toward the center of journal even in the steady state. The solutions for the equations of motion can be assumed as the Fourier series expansion. The equations of motion can be rewritten as the linear algebraic equations with respect to the Fourier coefficients. Then, stability of the grooved journal bearing can be calculated by Hill's infinite determinant. The periodic function of dynamic coefficients is derived using Fourier Fast Transform(FFT).The stability of journal bearing is determined as rotating speed increases and the stability of rotating grooved journal bearing is compared and discussed with the stability of stationary grooved journal bearing.

• 한국음향학회지
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• 제21권5호
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• pp.438-445
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• 2002

본 논문에서는 격자 트랜스버설 결합 (LTJ) 적응필터를 시변 변환영역 적응필터 관점에서 해석함으로써 필터계수보상의 필요성을 보다 쉽고 일반적으로 해석하였다. 또한, 음성 신호가 단구간에서 정적이라는 특성을 이용하여 필터계수 보상을 위한 계산량을 감소시킬 수 있는 방법을 제안하였으며, 모의 음성신호와 실제 음성신호를 사용한 실험을 통하여 효용성을 입증하였다. 제안된 적응필터는 필터계수 보상을 위한 계산량이 95% 감소되었으며, 1000탭을 사용하는 음향반향제거기의 경우 전체 시스템의 계산량을 82% 감소시킬 수 있다.

• Structural Engineering and Mechanics
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• 제42권6호
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• pp.849-866
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• 2012

Single span historic bridges often contain non-prismatic members identified with a varying depth along their span lengths. Commonly, the symmetric parabolic height variations having the constant haunch length ratio of 0.5 have been selected to lower the stresses at the high bending moment points and to maintain the deflections within the acceptable limits. Due to their non-prismatic geometrical configuration, their assessment, particularly the computation of fixed-end horizontal forces (FEFs) and fixed-end moments (FEMs) becomes a complex problem. Therefore, this study aimed to investigate the behavior of non-prismatic beams with symmetrical parabolic haunches (NBSPH) having the constant haunch length ratio of 0.5 using finite element analyses (FEA). FEFs and FEMs due to vertical loadings as well as the stiffness coefficients and the carry-over factors were computed through a comprehensive parametric study using FEA. It was demonstrated that the conventional methods using frame elements can lead to significant errors, and the deviations can reach to unacceptable levels for these types of structures. Despite the robustness of FEA, the generation of FEFs and FEMs using the nodal outputs of the detailed finite element mesh still remains an intricate task. Therefore, this study advances to propose effective formulas and dimensionless estimation coefficients to predict the FEFs, FEMs, stiffness coefficients and carry-over factors with reasonable accuracy for the analysis and re-evaluation of the NBSPH. Using the proposed approach, the fixed-end reactions due to vertical loads, and also the stiffness coefficients and the carry-over factors of the NBSPH can be determined without necessitating the detailed FEA.