• The Journal of the Acoustical Society of Korea
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• v.17 no.7
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• pp.61-73
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• 1998

라우드스피커의 비선형 음향특성을 해석하기 위하여 라우드스피커 다이아프램의 비 선형특성을 실험적으로 분석하였다. 라우드스피커를 집중질량계로 모델링하고, 출력소음이 없을 때 적용이 가능한 하모닉 발란스법과 출력소음이 있을 때도 적용할 수 있는 통계적 방 법인 라그란지 배수법을 사용하여 비선형 매개변수를 규명하였다. 70Hz 이하의 주파수 영역 에서는 라그란지 배수법이 2차 하모닉 왜곡특성에서 상대적으로 좋은 결과를 보였으며, 3차 하모닉 왜곡특성에서는 하모닉 발란스법이 실험결과와 잘 일치하였다. 전압가진 및 전류 가 진실험을 통하여, 일반화된 주파수 응답함수를 유도하였고 하모닉 왜곡 및 상호변조 특성을 고찰하였다. 고차 주파수 응답특성은 라우드스피커 비선형 매개변수의 변동에 따른 다이아 프램의 비선형특성을 해석하는데 유용한 수단이 될 수 있음도 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.709-715
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• 2011

Harmonic drives have been widely used in combination with joint torque sensors in order to facilitate accurate manipulator control. A harmonic drive causes a torque ripple because of its structural characteristics, and this torque ripple tends to deteriorate the performance of a controller or observer that uses torque sensors. This paper proposes a switching notch filter for reducing the torque ripple caused by a harmonic drive in a joint torque sensor; the functioning of this filter is based on the relationship between the frequency components of the torque ripple and the rotational velocity of the harmonic drive. The proposed switching notch filter is advantageous in that it requires less computational load and does not necessitate additional circuits or structures. Various experiments demonstrate that the proposed filter has good filtering performance, fast response, and good switching stability.

• Proceedings of the KIPE Conference
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• 2017.11a
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• pp.3-4
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• 2017

컨버터 제어를 위한 피크 전류 모드는 기존의 전류 모드 제어 기법에 비해 빠른 응답과 간단한 구조로 인해 많은 컨버터 애플리케이션에서 사용된다. 그러나 듀티가 0.5를 초과하면, 서브 하모닉 발진이 전류에서 발생한다. 이러한 현상을 방지하기 위해 제어기를 안정적으로 동작 할 수 있도록 보상 기울기를 추가 한다. 그러나 기울기 보상의 방법은 구조를 복잡하게 만들고 출력 전압이 가변적 일 때 때때로 기울기를 변화시켜야 하는 문제가 있다. 따라서 본 논문에서는 기울기 보상 없이 새로운 하이브리드 모드 전류 제어 방법을 제안한다. 밸리 전류 모드에서 트레일 링 에지 변조를 사용하는 제안 된 방법에서, 서브 하모닉 발진 문제는 쉽게 해결 될 수 있다. 제안 된 제어기는 Psim 시뮬레이션에 의해 검증된다.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.6
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• pp.124-129
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• 2018

A non-linear vibration isolation system which is composed of a non-linear spring and a linear damper was proposed in past research. When the support of the isolation system is excited harmonically, the response component of the isolation system mass at the excitation frequency has been calculated approximately using the harmonic balance method. The response was approximated by a single mode, and the result was compared with a numerical result which is assumed as an accurate one. Next, the response was approximated by two modes, and the result was compared with the former one.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.199-201
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• 2003

멀티미디어 서비스는 미디어 오브젝트의 대용량 특성으로 인해 클라이언트에게 서비스를 수행할 때 QoS를 보장하기 어렵다. 이러한 문제를 해결하기 위한 많은 연구가 진행되었는데 이중 사용자의 요구에 대한 적절한 응답시간과 서버의 부하를 줄이기 위한 목적으로 주기적인 멀티캐스트가 제안되었다. 하지만 오브젝트를 세그먼트로 나누는 이 멀티캐스트 정책은 세그먼트 개수의 증가에 따라 서버의 작업부하가 커지게 되는 단점을 가진다. 따라서 본 논문에서는 주기적인 멀티캐스트를 수행하는 서버의 작업부하를 줄이기 위해 스카이스크래퍼 멀티캐스트와 하모닉 멀티캐스트를 통해 서버의 휴지시간을 유도하고, 이에 따라 서버가 멀티캐스팅하는데 이용되는 시간을 감소시키는 멀티캐스트 정책을 제안한다.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.6
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• pp.23-28
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• 2020

A non-linear vibration isolation system composed of a non-linear spring and a linear damper was presented in a previous study. The advantage of the proposed isolator is the simple structure of the system. When the base of the isolator is harmonically excited, the response component of the mass at the excitation frequency was approximated using three different methods: linear approximation, harmonic balance, and higher-order frequency response functions (FRFs). The method using higher-order FRFs produces significantly more accurate results compared with the other methods. The error between the exact and approximate responses does not increase monotonously with the excitation amplitude and is less than 2%.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.2
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• pp.141-147
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• 2012

Engine mount is used to soften the impact of bumper with elasticity recovery and damping capacity. Inner noise and vibration to influence the comfortableness for passenger cause the engine to the chattering phenomenon. In this study, structural analysis can be done by engine mounts designed with 3D modelling. Natural frequencies and harmonic responses are analyzed by using models with some kinds of configurations. When the simulation model is applied by the force of 600N within the range of natural frequencies, the magnitude of deformation becomes 0 to 3mm. As the number of holes around inside mount increases, the capability of vibration absorption and durability becomes larger. In case of 5holes around inside mount, it can be safest on durability. The life of mount becomes larger by changing the configuration of model. The engine mount improved with durability can be designed through the result of simulation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.6
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• pp.687-695
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• 2021

With the recent occurrence of large-scale earthquakes in Korea, the importance of seismic design has greatly increased. Seismic design standards stipulate that dynamic time history analysis be performed for important or special structures. In the seismic analysis and design of such structures, determining a rational design input seismic wave is a very important factor in ensuring the reliability of the analysis and design. In the seismic design standards, rational design seismic waves must reflect the characteristics of the area (fault) and satisfy the design response spectrum for each seismic performance level. This requirement can be partially satisfied by modifying the actual seismic wave measured in the area (fault) according to the design response spectrum. In this study, a method of correcting and generating seismic wave time histories according to the design response spectrum based on actual measured seismic waves using the harmonic wavelet transform was proposed. To examine the applicability of the proposed technique, the technique was applied to earthquakes of magnitude 5.8 and 5.4, respectively, that occurred in Gyeongju (2016) and Pohang (2017), and the seismic wave time histories corresponding to the design response spectrum were modified and generated.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.4
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• pp.69-74
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• 2013

According to the axial torsion applied at power transmission and the vibration from the roughness of road surface, this paper analyzes the stresses on two kinds of universal joint model. As stress and deformation at model 2 becomes smaller than model 1 on structural analysis, model 2 is more stabilized than model 1. The natural frequencies at model 1 and 2 are 7,040 and 9,540 Hz respectively. As the natural frequency range of model 2 becomes higher than model 1, model 2 becomes safer than model 1. Critical frequencies at these models are calculated through harmonic response analyses. On critical frequencies at model 1 and 2, the stress at model 2 becomes lower than 2 times as much as model 1 and the deformation at model 2 becomes lower than 4 times as much as model 1. Model 2 on durability is thought to become better than model 1. This study result is applied with the design of safe universal joint and it can be useful to improve the durability by predicting prevention against the deformation due to its vibration.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.1
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• pp.126-134
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• 2014

This study investigates the structural strength analysis due to rib thickness of lower arm. At structural analysis, model 1 has the most deformation by comparing three models. As most equivalent stress is shown at the part connected with wheel knuckle, the strength becomes weaker in cases of three models. At fatigue analysis, model 1 becomes most unstabilized among three models. Model 3 has most fatigue life and the next model is model 2. The range of maximum harmonic response frequencies becomes 140 to 175Hz in cases of three models. Because the critical frequency at model 3 becomes highest among three models but the stress exceeds yield stress, model 3 becomes most unstabilized at vibration durability. As models 1 and 2 has less than yield stress, these models become stabilized. Model 2 becomes most favorable by comparing three models at structural, fatigue and vibration analyses. This study result can be effectively utilized with the design of lower arm by investigating prevention against damage and its strength durability.