• Transactions on Electrical and Electronic Materials
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• 제18권5호
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• pp.287-297
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• 2017

Novel power system stabilizers (PSSs) have been proposed to effectively dampen low frequency oscillations (LFOs) in multi-machine power systems and have attracted increasing research interest in recent years. Due to this attention, recently, fractional order controllers (FOCs) have found new applications in power system stability issues. Here, a tilt-integral-derivative power system stabilizer (TID-PSS) is proposed to enhance the dynamic stability of a multi-machine power system by providing additional damping to the LFOs. The TID is an extended version of the classical proportional-integral-derivative (PID) applying fractional calculus. The design of the proposed three-parameter tunable TID-PSS is systematized as a nonlinear time domain optimization problem in which the tunable parameters are adjusted concurrently using a modified group search optimization (MGSO) algorithm. An integral of the time multiplied squared error (ITSE) performance index is considered as the objective function. The proposed stabilizer is simulated in the MATLAB/SIMULINK environment using the FOMCON toolbox and the dynamic performance is evaluated on a 3-machine 6-bus power system. The TID-PSS is compared with both classical PID-PSS (PID-PSS) and conventional PSS (CPSS) using eigenvalue analysis and time domain simulations. Sensitivity analyses are performed to assess the robustness of the proposed controller against large changes in system loading conditions and parameters. The results indicate that the proposed TID-PSS provides the better dynamic performance and robustness compared with the PID-PSS and CPSS.

• Earthquakes and Structures
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• 제14권3호
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• pp.215-227
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• 2018

Supplemental passive control devices are widely considered as an important tool to mitigate the dynamic response of a building under seismic excitation. Nevertheless, a systematic method for strategically placing dampers in the buildings is not prescribed in building codes and guidelines. Many deterministic and stochastic methods have been proposed by previous researchers to investigate the optimum distribution of the viscous dampers in the steel frames. However, the seismic performances of the retrofitted buildings that are under large earthquake intensity levels or near collapse state have not been evaluated by any seismic research. Recent years, an increasing number of studies utilize genetic algorithms (GA) to explore the complex engineering optimization problems. GA interfaced with nonlinear response history (NRH) analysis is considered as one of the most powerful and popular stochastic methods to deal with the nonlinear optimization problem of damper distribution. In this paper, the effectiveness and the efficiency of GA on optimizing damper distribution are first evaluated by strong ground motions associated with the collapse failure. A practical optimization framework using GA and NRH analysis is proposed for optimizing the distribution of the fluid viscous dampers within the moment resisting frames (MRF) regarding the improvements of large drifts under intensive seismic context. Both a 10-storey and a 20-storey building are involved to explore higher mode effect. A far-fault and a near-fault earthquake environment are also considered for the frames under different seismic intensity levels. To evaluate the improvements obtained from the GA optimization regarding the collapse performance of the buildings, Incremental Dynamic Analysis (IDA) is conducted and comparisons are made between the GA damper distribution and stiffness proportional damping distribution on the collapse probability of the retrofitted frames.

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

• 한국공간구조학회논문집
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• 제12권2호
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• pp.65-72
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• 2012

본 연구에서는 비틀림 거동을 일으키는 편심구조물의 효율적인 제어를 위한 비틀림 강성을 가지는 동조질량감쇠기의 제어성능을 검토하고자 한다. 이를 위하여 지진하중을 받는 편심구조물에 동조질량감쇠기의 설치위치와 비틀림강성에 따른 제어성능을 평가한다. 반복되는 시간이력해석시 소요되는 해석시간을 줄이기 위하여 등가해석 모델을 사용하였고 비비례감쇠시스템인 동조질량감쇠가 설치된 구조물의 해석을 효율적으로 수행할 수 있었다. 본 연구를 통하여 일반적인 동조질량감쇠기에서 무시되어온 동조질량감쇠기의 비틀림 속성이 비틀림 거동이 발생하는 편심구조물에서는 효과적일 수 있음을 검증하였다. 그리고 편심구조물의 경우에는 동조질량감쇠기의 최적 설치 위치가 구조물 평면의 중심이 아닐 수 있음을 확인하였다.

• 농업과학연구
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• 제50권4호
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• pp.773-784
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• 2023

In this study, we developed a dynamic model and steering controller model for an autonomous tractor and evaluated their performance. The traction force was measured using a 6-component load cell, and the rotational speed of the wheels was monitored using proximity sensors installed on the axles. Torque sensors were employed to measure the axle torque. The PI (proportional integral) controller's coefficients were determined using the trial-error method. The coefficient of the P varied in the range of 0.1 - 0.5 and the I coefficient was determined in 3 increments of 0.01, 0.05, and 0.1. To validate the simulation model, we conducted RMS (root mean square) comparisons between the measured data of axle torque and the simulation results. The performance of the steering controller model was evaluated by analyzing the damping ratio calculated with the first and second overshoots. The average front and rear axle torque ranged from 3.29 - 3.44 and 6.98 - 7.41 kNm, respectively. The average rotational speed of the wheel ranged from 29.21 - 30.55 rpm at the front, and from 21.46 - 21.63 rpm at the rear. The steering controller model exhibited the most stable control performance when the coefficients of P and I were set at 0.5 and 0.01, respectively. The RMS analysis of the axle torque results indicated that the left and right wheel errors were approximately 1.52% and 2.61% (at front) and 7.45% and 7.28% (at rear), respectively.

• 한국균학회지
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• 제20권4호
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• pp.337-346
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• 1992

길항균 Trichoderma spp.가 입고병 및 식물토양병 방제에 효과적이었으므로 T. hamatum strain Tr-5와 Rhizoctonia solani 사이의 토양근권내의 상호작용을 구명하고, 생물학적 방제로서의 활용성을 알고저 기초적인 실험을 하였다. 길항성이 우수한 Trichoderma spp.의 토양내 분포비를 구명하고저 채집한 토양시료에서 길항균과 토양 미생물의 분포를 조사하였다. 전세균, 전진균, 방선균 및 Trichodema spp.의 분포비는 65%, 8.8%, 25.9% 및 0.28%로 세균이 많고 Trichoderma spp.의 분리비는 가장 적었다. Trichoderma spp.를 분리하여 동정한 결과 T. koninggii, T. pseudokoninggii, T. aureoviride, T. hamatum 및 T. viride의 5종이 동정되었고, 이중 균주 Tr-5인 T. hamatum을 공시하여 균기생성여부를 관찰한 결과 R. solani에 대한 기생성을 관찰하였으며 효소적으로 균사가 용균되어 파괴됨을 관찰하였다. Trichoderma spp.의 토양내 발아력을 조사한 결과 자연토양에서 Trichoderma spp. 모든 종은 $1.7{\sim}7.3$ 이내의 발아력을 나타내었고, 살균토양에서는 90% 이상의 포자발아력을 나타내어 자연토양에서 Trichoderma 정균현상이 관찰되었다. 길항력이 있는 T. koninggii, T. pseudokoninggii, T. hamatum 및 T. viride 등 4균주의 토양근권내 완두뿌리 근권점유율실험에서 4종 균주 모두는 토양깊이 1cm 범위까지는 점유율이 크게 나타났으나 $2{\sim}3\;cm$에 서는 분포수가 감소하였고 4 cm 이하에서는 뿌리 점유분포수가 크게 감소하였다. 인삼근을 심은 폿트실험에서 Fusarium solani, Cylindrocarpon destructans, Rhizoctonia solani균의 단독처리구에 비해 길항력이 있는 T. hamatum Tr-5 처리구에서는 근부현상이 감소하였다.