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정태건(Tae-Gun Jeong) 한국산학기술학회 2018 한국산학기술학회논문지 Vol.19 No.2
대형트럭으로 견인되는 트레일러는 무게중심이 일반 차량에 비해 상대적으로 높기 때문에 전복사고 위험이 높게 된다. 곡선 주행 구간에서 차체를 기울여 곡선부의 주행속도를 향상시키는 원리를 적용하는 틸팅 시스템은 고속철도 차량에서 먼저 그 개념이 연구되고 사용되어 왔는데, 이 논문에서는 일반 대형트럭의 트레일러 적재함에 이 틸팅 시스템을 적용함으로써 아주 작은 틸팅각의 변화로도 급회전 시 주행 안정성을 크게 개선할 수 있는 가능성에 대해 연구하였다. 틸팅 가능한 트레일러의 동역학적 모델을 사용하여 선회주행 시 운동 관계식을 유도함으로써 주어진 도로 선회반경과 하중조건에 대해 원심력 효과와 수직력의 균형으로 전복임계속도를 결정할 수 있었다. 본 논문에서는 보수적인 기준을 선택하여 한쪽 바퀴가 지면으로부터 떨어지는 순간을 전복임계상태로 정의하였다. 실제로 틸팅 시스템을 작동시키기 위해서는 조향각과 주행속도로부터 최적 틸팅각을 계산해야 한다. 트레일러가 달린 대형트럭을 간단하게 모델링하고 시뮬레이션을 통해 곡선주행시 차량의 틸팅각에 따른 전복임계속도의 변화를 분석하고, 틸팅의 효과를 입증하였다. Rollover is a major concern for vehicles with a higher center of gravity and for improving driving performance. This study investigates a tilting system to prevent rollover, which was successfully implemented for high-speed trains. It may be useful to apply the concept of the tilting system to a large truck such as a trailer. Even a small adjustment in the tilting angle can improve the driving stability during a steep turn. The equation of motion was derived from a dynamic model of the trailer with the tilting system. The balance of the centrifugal force and normal force determines the rollover critical speed for a given radius of the turn and load. To obtain a more conservative criterion, the rollover critical state was defined as the instant when any side wheel loses contact with the road. To actuate the tilting system, the optimal tilting angle must be calculated from the steering angle and the vehicle speed. Using a simplified model of a large truck, the effects of the tilting angle and load on the rollover critical speed were investigated.
재배치 시간-주파수 해석을 이용한 슬라이더 공기베어링의 비정상 거동 연구
정태건(Jeong, Tae-Gun) 한국소음진동공학회 2006 한국소음진동공학회 논문집 Vol.16 No.3
Frequency spectrum using the conventional Fourier analysis gives adequate information about the dynamic characteristics of the slider air bearing for the linear and stationary cases. The intermittent contacts for the extremely low flying height, however, generate nonlinear and nonstationary vibration at the instant of contact. Nonlinear dynamic model should be developed to simulate the impulse response of the air bearing during slider-disk contact. Time-frequency analysis is widely used to investigate the nonstationary signal. Several time-frequency analysis methods are employed and compared for the slider vibration signal caused by the impact against an artificially induced scratch on the disk. The representative Wigner-Ville distribution leads to the severe interference problem by cross terms even though it gives good resolution both in time and frequency. The smoothing process improves the interference problem at the expense of resolution. In order to get the results with good resolution and little interference, the reassignment method is proposed. Among others the reassigned Gabor spectrogram shows the best resolution and readability with negligible interference.
비정상 AE 진동감시 신호의 에너지 분포특성과 시간-주파수 해석
정태건(Jeong, Tae-Gun) 한국소음진동공학회 2012 한국소음진동공학회 논문집 Vol.22 No.3
Conventional Fourier analysis can give only limited information about the dynamic characteristics of nonstationary signals. Instead, time-frequency analysis is widely used to investigate the nonstationary signal in detail. Several time-frequency analysis methods are compared for a typical acoustic emission burst generated during the impact between a ferrite ceramic and aluminum plate. This AE burst is inherently nonstationary and random containing many frequency contents, which leads to severe interference between cross terms in bilinear convolution type distributions. The smoothing and reassignment processes can improve the readability and resolution of the results. Spectrogram and scalogram of the AE burst are obtained and compared to get the characteristics information. Renyi entropies are computed for various bilinear time-frequency transforms to evaluate the randomness. These bilinear transforms are reassigned by using the improved algorithm in discrete computation.
조합공진 영역에서 감쇠의 영향을 고려한 비선형 진동 응답 특성
정태건(Jeong, Tae-Gun) 한국소음진동공학회 2010 한국소음진동공학회 논문집 Vol.20 No.9
Damping may change the response characteristics of nonlinear oscillations due to the parametric excitation of a thin cantilever beam. When the natural frequencies of the first bending and torsional modes are of the same order of magnitude, we can observe the one-to-one combination resonance in the perturbation analysis depending on the characteristic parameters. The nonlinear behavior about the combination resonance reveals a chaotic motion depending on the natural frequencies and damping ratio. We can analyze the chaotic dynamics by using the eigenvalue analysis of the perturbed components. In this paper, we derived the equations for autonomous system and solved them to obtain the characteristic equation. The stability analysis was carried out by examining the eigenvalues. Numerical integration gave the physical behavior of each mode for given parameters.
AE 신호를 이용한 HDD 슬라이더 공기베어링의 부상상태 측정
김재직,정태건,Kim, Jae-Jic,Jeong, Tae-Gun 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.9
The AE measurement is one of the most convenient methods for detecting contacts between the slider and the disk. The AE method has been widely used in the investigation of the tribology of sliding interfaces due to its convenience. We examined the relationship between the AE signal and the flying height of a slider. We investigated the influence of the disk linear velocity on the AE rms signal by using the AE measurement system. The experiment also gives the relationship between the take-off velocity and the disk surface conditions. To investigate the behavior of the slider further, the variances of the AE signals are analyzed. The experimental results indicate that the increase in the magnitude of the AE rms signal does not necessarily mean the slider/disk contacts.