• The Journal of the Acoustical Society of Korea
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• 제18권4E호
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• pp.10-19
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• 1999

Psychophysical approaches to the room acoustics have been made in number of researches. The present study is looking at whether the listener's perception of frequency change in rooms are dependent on the acoustics of a listening environment. P(C)s for frequency change in short tones were measured in different listening conditions. Two experiments were carried out to investigate the influence of room acoustics on the listener's perception of frequency change, and its implication for evaluating the acoustics of listening environments were examined and discussed. It was found that the temporal and spectral contents of reflections from room surfaces might be an important factor which influenced the listener's perception of frequency change in a reverberant sound field. This implicates that psychophysical approach by measuring listener's frequency change perception might be an useful tool for evaluating room acoustics. However, cares should be taken, since some individual differences were found to exist with respect to the direction of frequency change.

• 한국시뮬레이션학회논문지
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• 제7권2호
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• pp.115-123
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• 1998

A simulation is performed to investigate the effect of the pipe supports on the change of the natural frequencies of curved pipe systems containing fluid flow, for different elbow angles and geometry of the pipe systems. Based upon the Hamilton's principle, the equations of motions are derived, and the finite element equation is constructed to solve the corresponding eigenvalue problem. The angles of elbows do not affect the change of the fundamental natural frequency, but affect the change of the third or higher natural frequencies. Without any support, the change of the fundamental natural frequency due to the geometric change is smaller than the change of the second or higher natural frequencies. The more curve parts exist in the pipe system, the less change of lower frequency range, compared with the change of higher frequency range, is observed. Spring supports can be used to reduce the fundamental natural frequency, without change of the second or higher natural frequencies. To avoid resonance, which is critically dangerous from the view point of structural dynamics, the mechanical properties such as stiffness or the location of pipe supports are need to be changed to isolate the natural frequencies from the frequency range of dominant vibration modes.

• 한국산업융합학회 논문집
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• 제8권2호
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• pp.97-104
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• 2005

Usually, propagation attenuation of millimeter wave occurs by rainfall, snowfall, temperature, effect of pressure of air. In 60GHz wave band wireless communication network, temperature change becomes big factor of propagation loss department. Also, temperature change causes disturbance of 60GHz frequency at transceiver. In this study, we used 60GHz transceiver and found propagation loss of wireless path and operating frequency disturbance characteristics. In transceiver that there is no temperature compensated device, operating frequency of TX changed by 60.865GHz at temperature of $-5^{\circ}C$, and appeared by 60.730GHz when is $50^{\circ}C$. Therefore, operating frequency change width by temperature change are about 100MHz, greatly. But, in transceiver that there is temperature compensated device, operating frequency of TX changed by 60.830GHz at temperature of $-5^{\circ}C$, and appeared by 60.710GHz when is $50^{\circ}C$. Therefore, operating frequency change width by temperature change are about 20MHz. According to these result, we constructed between buildings examination wireless site for point to point wireless communication using 60GHz band transceivers who have do temperature compensated device, and investigated data transmission characteristics about ambient temperature change. Therefore, if use transceiver that have temperature compensated device, may overcome the wireless transmission error in 60GHz band wireless communication LAN networks despite of ambient temperature change.

• 한국시뮬레이션학회논문지
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• 제24권3호
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• pp.45-54
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• 2015

본 논문에서는 기어감속 서보시스템의 모터입력전압 크기를 적절히 감소시키면 모터입력전압에 대한 모터각속도에서 나타나는 주파수응답특성에 미치는 백래시 영향이 매우 커지게 됨을 보여 주였다. 또한 주파수응답선도에서 나타나는 반공진 및 공진주파수 변화량을 관찰하여 기어감속 서보시스템 내 기어 백래시 변화를 감지할 수 있는 방법의 유용성을 이론적, 시뮬레이션 및 실험적으로 검증하였다. 반공진주파수 변화가 공진주파수 변화 보다 안정적으로 계측될 수 있으므로 백래시 크기 변화감지 시 반공진주파수 변화량 관찰이 좀 더 유용하며, 공진주파수는 모터입력전압을 충분히 감속시켜야 급격한 변화를 관찰할 수 있음을 보여주었다. 본 연구는 기어감속 서보시스템 내 백래시 크기 변화 감지에 대한 향후 연구에 있어서 유용하게 사용될 수 있을 것이라고 생각한다.

• 전기전자학회논문지
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• 제25권3호
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• pp.534-539
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• 2021

본 논문에서는 유도 가열코일의 인덕턴스 변화 환경에서 스위칭주파수를 가변하여 최대 가열 전력이 전달될 수 있는 유도 가열 방식을 제안하였다. 가열코일내 피 가열체 종류 및 가열코일과의 근접도에 따라 공진회로의 공진주파수가 변화하게 되며, 공진주파수와 스위칭주파수 관계에 따라 유도가열기 소자의 파손 또는 손실이 발생하여 최대 전력 전달이 어려울 수 있다. 공진주파수의 변화에 따른 가열 전력을 감지하여 최대 전력 전달이 유지되도록 스위칭주파수를 가변하도록 하였다. 공진 주파수 변화에 대응하는 스위칭주파수 가변에 따라 요구하는 출력 변화 범위내로 제어될 수 있는 제안된 방식의 결과를 통하여 거의 일정한 출력전력(0.43 dB 이내) 전달이 가능한 스위칭주파수 가변특성을 갖는 유도가열기의 전력 효율성을 확보할 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제10권2호
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• pp.496-503
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• 2015

In order to let a wind generator (WG) support the frequency control of a power system, a conventional inertial control algorithm using the rate of change of frequency (ROCOF) and frequency deviation loops was suggested. The ROCOF loop is prevailing at the initial stage of the disturbance, but the contribution becomes smaller as time goes on. Moreover, its contribution becomes negative after the frequency rebound. This paper proposes an inertial control algorithm of a wind power plant (WPP) using the maximum ROCOF and frequency deviation loops. The proposed algorithm replaces the ROCOF loop in the conventional inertial control algorithm with the maximum ROCOF loop to retain the maximum value of the ROCOF and eliminate the negative effect after the frequency rebound. The algorithm releases more kinetic energy both before and after the frequency rebound and increases the frequency nadir more than the conventional ROCOF and frequency loops. The performance of the algorithm was investigated under various wind conditions in a model system, which includes a doubly-fed induction generator-based WPP using an EMTP-RV simulator. The results indicate that the algorithm can improve the frequency drop for a disturbance by releasing more kinetic energy.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전기물성,응용부문
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• pp.223-225
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• 2005

An external electrode fluorescent lamps (EEFLs) have the advantage of a long lifetime in the early stages of the study on plasma discharge, interest in the lamp continues. Studies on the operation of external electrode fluorescent lamps have focused mainly on its use of a type of high frequency (MHz). By performing high brightness using a square wave operation method with the low frequency below 100kHz, which is applied to a narrowed tube type lamp that has several mm of lamp diameter, an EEFL presented the possibility of using it as a light source for backlights. However, because an EEFL generates plasma using wall charges, which considers the impedance characteristics of glass based on the structural principle in discharge, it can be significantly affected by frequency. Thus, this study verifies the change in the characteristics of electromagnetic fields according to the change in frequency through a Maxwell's electromagnetic field simulation and examines the relationship between the change in the EEFL frequency and brightness by measuring the optical characteristics. In addition, the characteristics of the transformation of energy orbits were verified by investigating the characteristics of the wavelength according to the change in frequency through the OES.

• 대한후두음성언어의학회지
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• 제9권1호
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• pp.11-16
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• 1998

Background and Objectives : Electrolarynx has been used as one of the methods of rehabilitation for the laryngectomees. Previous electrolarynx could not alter frequency and intensity simultaneously. This institute developed an electrolarynx named "Evada" using FSR(force sensing resistor) sensor, which can control the frequency(and/or intensity) simultaneously. This study was performed for the normal control and laryngectomees with three types of electrolarynx (Evada, Servox-inton, Nu-vois) to reveal functional characteristics of Evada Materials and Methods : five laryngectomees and five normal adults were made to express there sentences(discriptive sentence, "You stay here" ; question sentence, "You stay here？" ; exclamation sentence, "You!! stay here!"), using three types of electrolarynx. Frequency change and intensity change from first and last vowel was calculated in three sentences and analyzed statistically by paired T-test. Results : The frequency change in the question sentence and exclamation sentence was more prominent in Evada than in Servox-inton and Nu-vois. The intensity change in the question sentence and exclamation sentence was also more prominent in Evada than in Servox-inton and Nu-vois. Conclusions : Evada could control frequency and intensity simultaneously and control degree of frequency(and/or intensity) according to the pressing force into the button. Evada could adjust continuously frequency and intensity during conversation. So, Evada is better in producing intonation and contrastive stress than Nu-vois and Servox-inton.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 광주전남지부
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• pp.75-78
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• 2006

An external electrode fluorescent lamps (EEFLs) have the advantage of a long lifetime in the early stages of the study on plasma discharge, interest in the lamp continues. Studies on the operation of external electrode fluorescent lamps have focused mainlyon its use of a type of high frequency (MHz). By performing high brightness using a square wave operation method with the low frequency below 100kHz, which is applied to a narrowed tube type lamp that has several mm of lamp diameter, an EEFL presented the possibility of using it as a light source for backlights. However, because an EEFL generates plasma using wall charges, which considers the impedance characteristics of glass based on the structural principle in discharge, it can be significantly affected by frequency. Thus, this study verifies the change in the characteristics of electromagnetic fields according to the change in frequency through a Maxwell's electromagnetic field simulation and examines the relationship between the change in the EEFL frequency and brightness by measuring the optical. characteristics. In addition, the characteristics of the transformation of energy orbits were verified by investigating the characteristics of the wavelength according to the change in frequency through the OES.

• Smart Structures and Systems
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• 제23권2호
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• pp.107-122
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• 2019

As one of the most important parameters in structural health monitoring, structural frequency has many advantages, such as convenient to be measured, high precision, and insensitive to noise. In addition, frequency-change-ratio based method had been validated to have the ability to identify the damage occurrence and location. However, building a precise enough finite elemental model (FEM) for the test structure is still a huge challenge for this frequency-change-ratio based damage detection technique. In order to overcome this disadvantage and extend the application for frequencies in structural health monitoring area, a novel method was developed in this paper by combining the cross-model cross-mode (CMCM) model updating algorithm with the frequency-change-ratio based method. At first, assuming the physical parameters, including the element mass and stiffness, of the test structure had been known with a certain value, then an initial to-be-updated model with these assumed parameters was constructed according to the typical mass and stiffness distribution characteristic of shear buildings. After that, this to-be-updated model was updated using CMCM algorithm by combining with the measured frequencies of the actual structure when no damage was introduced. Thus, this updated model was regarded as a representation of the FEM model of actual structure, because their modal information were almost the same. Finally, based on this updated model, the frequency-change-ratio based method can be further proceed to realize the damage detection and localization. In order to verify the effectiveness of the developed method, a four-level shear building was numerically simulated and two actual shear structures, including a three-level shear model and an eight-story frame, were experimentally test in laboratory, and all the test results demonstrate that the developed method can identify the structural damage occurrence and location effectively, even only very limited modal frequencies of the test structure were provided.