• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.113-120
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• 2008

One-dimensional site response analysis is widely used to simulate the seismic site effects. The equivalent linear analysis, which is the most widely used type of site response analysis, is essentially a linear method. The method applies constant shear modulus and damping throughout the frequency range of the input motion, ignoring the dependence of the soil response on the loading frequency. A new type of equivalent linear analysis method that can simulate the frequency dependence of the soil behavior via frequency-strain curve was developed. Various forms of frequency-strain curves were proposed, and all curves were asserted to increase the accuracy of the solution. However, its validity has not been extensively proven and the effect of the shape of the frequency-strain curve is not known. This paper used two previously proposed frequency-strain curves and three additional curves developed in this study to evaluate the accuracy of the frequency-dependent equivalent linear method and the influence of the shape of the frequency-strain curves. In the evaluation, six recordings from three case histories were used. The results of the case study indicated that the shape of the frequency-strain curve has a dominant influence on the calculated response, and that the frequency dependent analysis can enhance the accuracy of the solution. However, a curve that results in the best match for all case histories did not exist and the optimum curve varied for each case. Since the optimum frequency-strain curve can not be defined, it is recommended that a suite of curves be used in the analysis.

• Journal of Korean Society of Steel Construction
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• v.27 no.2
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• pp.181-193
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• 2015

High-frequency staircases are widely used nowadays to meet aesthetics and functionality needed in modern architecture. Unfortunately, no design guide is available in domestic practice to predict response or evaluate the vibration performance of high-frequency staircases. SCI-P354 published by the Steel Construction Institute of UK provides the formula for effective impulsive force. However, this formula was shown to overestimate the response of high-frequency staircases excited by fast ascending and descending over 2.2Hz pace frequency because it was developed based on the walking test in a slow pace frequency. This study proposes a semi-analytical formula to predict the response of stiff staircases based on analytical and experimental studies of response acceleration for various walking frequencies covering 1.4~4.5Hz.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.7
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• pp.1331-1338
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• 2011

This paper proposes a method for frequency control of islanded microgrid with battery energy storage system. For frequency control of islanded microgrid, battery energy storage system uses a phase locked loop algorithm with positive sequence components for a fast frequency estimation. Microgrid is a power system with small inertia because it has small capacity generators and inverter systems for renewable energy. So, Islanded microgrid's frequency varies fast and large as small generation and load changes. To reduce frequency variation of islanded microgrid, it needs a device with fast frequency response. For fast frequency response, a fast frequency tracking is important. To show the validation of proposed fast frequency tracking algorithm, battery energy storage system with proposed algorithm is tested in microgrid pilot plant.

• Nutrition Research and Practice
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• v.4 no.1
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• pp.75-81
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• 2010

This study explored the conceptual framework of dieticians' intentions to recommend functional food and the mediating role of consumption frequency. A web-based survey was designed using a self-administered questionnaire. A sample of Korean dieticians (N=233) responded to the questionnaire that included response efficacy, risk perception, consumption frequency, and recommendation intention for functional foods. A structural equation model was constructed to analyze the data. We found that response efficacy was positively related to frequency of consumption of functional foods and to recommendation intention. Consumption frequency also positively influenced recommendation intention. Risk perception had no direct influence on recommendation intention; however, the relationship was mediated completely by consumption frequency. Dieticians' consumption frequency and response efficacy were the crucial factors in recommending functional foods. Dieticians may perceive risks arising from the use of functional foods in general, but the perceived risks do not affect ratings describing dieticians' intentions to recommend them. The results also indicated that when dieticians more frequently consume functional foods, the expression of an intention to recommend functional foods may be controlled by the salience of past behaviors rather than by attitudes.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.4
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• pp.463-468
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• 2015

High vibration of a low pressure (LP) turbine casing caused safety problems and life at the facility it was housed in. The main focus of this study was the cause of the high vibration in a low pressure turbine casing with manufacturing defects by frequency response analysis, compared with the results of experiments. Therefore, excited accelerations were obtained from the LP casing fundamental, and frequency responses were analyzed. The measurement and the modal analysis showed that the natural frequency of the LP turbine casing was 61.26 Hz and the excited frequency of the turbine rotor was 60.25 Hz. The manufacturing defect caused a decrease in the casing natural frequency and resulted in the high vibration of the casing because it moved close to the resonant frequency.

• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1345-1356
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• 2021

Damage to nuclear power plants causes human casualties and environmental disasters. There are electrical facilities that control safety-related devices in nuclear power plants, and seismic performance is required for them. The 2016 Gyeongju earthquake had many high-frequency components. Therefore, there is a high possibility that an earthquake involving many high frequency components will occur in South Korea. As such, it is necessary to examine the safety of nuclear power plants against an earthquake with many high-frequency components. In this study, the shaking table test of electrical facilities was conducted against the design earthquake for nuclear power plants with a large low-frequency components and an earthquake with a large high-frequency components. The response characteristics of the earthquake with a large high-frequency components were identified by deriving the amplification factors of the response through the shaking table test. In addition, safety of electrical facility against the two aforementioned types of earthquakes with different seismic characteristics was confirmed through limit-state seismic tests. The electrical facility that was performed to the shaking table test in this study was a motor control center (MCC).

• The Journal of the Acoustical Society of Korea
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• v.33 no.3
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• pp.184-190
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• 2014

Although it is ideal that the sound with the range of 20 ~ 20,000 Hz is produced by the loudspeaker system composing of only one loudspeaker unit, it is almost impossible now. Therefore, the audible frequency range is now produced by the loudspeaker system, which is consisted of more than two loudspeaker units. The multi-way loudspeaker system certainly requires a crossover filter, which is divided the audible frequency into low and high frequency ranges. The crossover frequency of filter usually is in the range of 1 ~ 4 kHz, the frequency range can largely affect to the sound articulation and quality. It is an example that the phase and amplitude at the crossover frequency can be different from each other, due to the variously reasons. Conversely, they can not produce the smooth frequency response due to the different distance between the two loudspeaker units and electrical properties. As a result, the sound articulation and quality can be degraded. Therefore, the phase and amplitude response at the crossover frequency has to be deeply considered, in order to exactly match the woofer and tweeter. In this study, it is proposed the methods which are the flat frequency and phase response to be obtained by adjusting of the delay time between loudspeaker units, and the choice of filter to be considered the roll-off properties of each unit. It is achieved the frequency response with ${\pm}1$ dB, and the sound articulation is also improved.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1439-1443
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• 2007

In this paper, vibration reduction techniques of a voice coil motor (VCM) actuator are presented for AFM imaging system. The damping coefficient of the actuator driven by VCM with a flexure hinge is quite low and it cause the about 30dB peak amplitude response at the resonance frequency. To decrease this peak response, we design and apply elliptical band-stop filters to xy and z axis VCM actuator. Frequency response of each actuator with filter is measured to verify the effect of the filters. As a sensor, capacitive sensor is used. Vibration reduction rate of the xy actuator with the filter is also measured while real AFM scanning condition. As another method, closed loop control with the capacitive sensor is applied to the xy axis actuator to add an electrical damping effect and vibration reduction rate measured. These vibration reduction rates with each method are compared. In the case of z axis actuator, the frequency response of force (gap) control loop is measured. For comparison, the frequency response using a conventional PID controller is also obtained. Finally, the AFM image of a standard grid sample is measured with the designed controller to analyze the effect in the AFM imaging.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.2
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• pp.83-93
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• 2020

Dynamic pressure transducer needs to be flush-mounted on hardware due to frequency response characteristics of pressure transmission system. However, it is sometimes necessary to be mounted in recessed configuration due to insufficient space for sensor installation and for protection of sensor from thermal damage. Dynamic response characteristics should be considered due to distortion of original dynamic pressure signal in the pressure transmission system. In this study, small perturbation model and 2nd order reduced model were compared with experiments and a guideline for selecting a frequency response model was suggested.

• Journal of Power Electronics
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• v.12 no.2
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• pp.317-325
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• 2012

Resonant immittance converter (RIC) topologies can transform a current source into a voltage source (Type-I RICs) and vice versa (Type-II RICs), thereby making them suitable for many power electronics applications. RICs are operated at a fixed frequency where the resonant immittance network (RIN) exhibits immittance conversion characteristics. It is observed that the low-frequency response of Type-II RINs is relatively flat and that the state variables associated with Type-II RINs affect the response only at the high frequencies in the vicinity of the switching frequency. The overall response of a Type-II RIC is thus dominated by the filter response, which is particularly important for the controller design. Therefore, an approximate equivalent circuit model and a small-signal model of Type-II RICs are proposed in this paper, neglecting the high-frequency response of Type-II RINs. While the proposed models greatly simplify and speed-up the analysis, it adequately predicts the open-loop transient and small-signal ac behavior of Type-II RICs. The validity of the proposed models is confirmed by comparisons of their results with those obtained from a cycle-by-cycle simulation and with an experimental prototype.