Chan-Jung Kim

Bio: Chan-Jung Kim is an academic researcher from Pukyong National University. The author has contributed to research in topics: Damper & Rotor (electric). The author has an hindex of 1, co-authored 2 publications receiving 12 citations.

Design sensitivity analysis of a Stockbridge damper to control resonant frequencies

Abstract: A Stockbridge damper system can control the aeolian vibrations in a transmission line by dissipating excitation energy through the self-excitation of the damper system. Therefore, locating these resonant frequencies is a critical design consideration for a Stockbridge damper to determine the efficiency of spectral energy dissipation. In this study, the design strategy of a damper was investigated after conducting a design sensitivity analysis of the resonant frequency of a Stockbridge damper that considered several design parameters, including length of the messenger wire, inertia of the counterweight, and gyration radius of the counterweight. The formulation of the design sensitivity analysis was performed using partial derivatives of the eigenvalues with respect to each design parameter over two resonant frequencies. The sensitivity formulations were validated through a case study of eigenvalues that considered a variation of up to ±30 % in the values of the design parameters. The design guidelines for a Stockbridge damper were derived from the sensitivity analysis results.

Frequency domain indirect identification of AMB rotor systems based on fictitious proportional feedback gain

Abstract: It is very difficult to directly identify an unstable system with uncertain dynamics from frequency domain input-output data. Hence, in these cases, closed-loop frequency responses calculated using a fictitious feedback could be more identifiable than open-loop data. This paper presents a frequency domain indirect identification of AMB rotor systems based on a Fictitious proportional feedback gain (FPFG). The closed-loop effect due to the FPFG can enhance the detectability of the system by moving the system poles, and significantly weigh the target mode in the frequency domain. The effectiveness of the proposed identification method was verified through the frequency domain identification of active magnetic bearing rotor systems.

Aeolian Vibration Control of Power Transmission Line Using Stockbridge Type Dampers — A Review

Abstract: Due to its inherent low damping, a power transmission line is prone to wind induced vibration. Vibration control is needed to suppress the aeolian vibration of the transmission-line to reduce the f...

Modal Damping Coefficient Estimation of Carbon-Fiber-Reinforced Plastic Material Considering Temperature Condition.

Abstract: Excellent mechanical properties of carbon-fiber-reinforced plastic material (CFRP) demonstrates many possibilities in industries using lightweight materials, but unlike isotropic materials, such as iron, aluminum, and magnesium, they show direction-sensitive properties, which makes it difficult to apply for them The sensitivity of a modal damping coefficient of a CFRP material over the direction of carbon fiber was examined on spectral input patterns in recent research, but the effect of temperature was not considered up to now To overcome this, uniaxial vibration tests were conducted using five simple specimens with different direction of carbon fiber in a CFRP specimen, the frequency response functions were experimentally determined and the modal damping coefficients were calculated It was revealed that the resonance point and the modal damping of the specimen changed according to the change in temperature condition Based on the experimental results, it was demonstrated that the theoretical frequency response function of the carbon composite material is a function of temperature, and it was confirmed that the nonlinear characteristic of the modal damping was the smallest under the 0 degree of direction of carbon fiber

Sensitivity Analysis of the Frequency Response Function of Carbon-Fiber-Reinforced Plastic Specimens for Different Direction of Carbon Fiber as Well as Spectral Loading Pattern.

Abstract: Carbon-fiber-reinforced plastic (CFRP) has been used in many industries owing to its excellent specific-strength characteristics; however, the control of its mechanical properties is difficult owing to the directivity nature of carbon fiber as well as the composition of layered structures. In addition, the damping coefficient of CFRP varies with spectral loading patterns under random and harmonic excitation owing to the high values of damping characteristics compared with conventional steel materials. A scaled sensitivity index was proposed to compare the magnitude of the frequency response function over two parameters of interest: the direction of the carbon fiber and the spectral loading pattern for CFRP specimens. Three specimens with different directions (0°, 45°, and 90°) were prepared and uniaxial excitation testing was conducted for two different spectral loading cases: random and harmonic. The summation of the frequency response was used to calculate the sensitivity index to eliminate the effects of the location of measurement data, and all sensitivity indexes were calculated using the measured responses. Finally, the sensitivity of each CFRP specimen was discussed for two cases, i.e., the direction of carbon fiber and the spectral loading pattern, using the scaled sensitivity index results.

Temperature-Dependent Dynamic Characteristics of Carbon-Fiber-Reinforced Plastic for Different Spectral Loading Patterns

Abstract: The dynamic properties of carbon-fiber-reinforced plastic (CFRP) can be efficiently estimated through a modal damping coefficient and a resonance frequency, and the modal parameters can be calculated using a frequency response function (FRF). The modal parameters used in an CFRP FRF are influenced by the carbon fiber direction, temperature, and spectral loading pattern, as well as the operating conditions. In this study, three parameters—temperature, spectral loading pattern, and carbon fiber direction—were selected as the influential factors for CFRP dynamics, and the sensitivity index formulation was derived from the parameter-dependent FRF of the CFRP structure. The derivatives of the parameter-dependent FRF over the three considered parameters were calculated from the measured modal parameters, and the dynamic sensitivity of the CFRP specimens was explored from the sensitivity index results for five different directional CFRP specimens. The acceleration response of a simple CFRP specimen was obtained via a uniaxial excitation test at temperatures ranging from −8 to 105 °C for the following two spectral loading cases: harmonic and random.