• 대한기계학회논문집A
• /
• 제21권11호
• /
• pp.1957-1964
• /
• 1997

Torsional vibration is to vibrate strongly when the ignition pulses of the engine is excited with natural frequency of driveline. Torsional vibration like this can cause various noises as rattle and booming. For this study multi-degree of freedom analysis model of torsional vibration, which is combined with mass moment of inertia and torsional spring, was developed toward two wheel drive, four wheel drive and torsional vibration characteristics were compared and analyzed through the natural frequences, mode shapes and frequency response characteristics which was acquired by the simulation of it. The pertinence of that model was proved by the field test and the outcome of the simulations coincided with feeling test. Therefore, four wheel drive simulation model is considered to be useful thing for reducing torsional vibration of driveline and developing full-time four wheel drive vehicles.

• 정보처리학회논문지B
• /
• 제8B권5호
• /
• pp.565-572
• /
• 2001

위치와 주파수 불확실성 곱이 작은 해석함수는 영상처리와 압축에 많은 장점이 있다. 지금까지의 불확실성원리에 기초하여 이 값을 계산하였으나, 이러한 측정은 최대 응답주파수가 0 이 아닌 인간시각필터에서 적절한 주파수 불확실성의 측정방법이 될 수 없다. 최대 응답을 갖는 주파수에 대한 주파수 불확실성을 계산하는 새로운 측정방법을 이용하여 결합유효폭을 유도하고자 한다. 결합변수가 커지면 많은 함수들의 결합유효폭이 0.5로 수렴하는 해석 결과를 얻었으며, 고려 대상 중에서 Gabor cosine 함수가 우수한 성능을 보였다.

• 한국해양공학회지
• /
• 제15권1호
• /
• pp.19-25
• /
• 2001

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures or ships is possible only when the fluid-structure interaction is understood, as the whole or part of the structure is in contact with water. This paper introduces two methods to find natural frequency in consideration of fluid-structure interaction, direct coupled vibration analysis and fluid-structure modal coupled vibration analysis. The purpose of this study is to analyze the vibration characteristic of a submerged vehicle to obtain the anti-vibration design data, which could be used in the preliminary design stage. The underwater pressure hull of submerged vehicle is used as the model of this study. The F.E.M. model is meshed by shell and beam elements. Also, considering the inner hull weight, the mass element is distributed in the direction of hull length. Numerical calculations are accomplished by using the commercial B.E.M. code. The characteristics of natural frequency, mode shape and frequency-displacement response are analyzed.

• Journal of Electrical Engineering and Technology
• /
• 제11권6호
• /
• pp.1556-1570
• /
• 2016

In the process of virtual inertia control (VIC), the frequency regulation capability of the directly-driven wind turbine with permanent-magnet synchronous generator (D-PMSG) on wind farm is related to its rotor kinetic energy and capacity margin. This paper proposes the method for assessing the D-PMSG frequency regulation capability and defining its coefficient according to the operating state of wind power generators. In addition, the calculating method of parameters in VIC is also discussed according to the principles of primary frequency regulation and inertia response of synchronous generators. Then, by introducing the capability coefficient into the proportion-differential virtual inertia control (PD-VIC) for power coordination, a coordinated virtual inertia control (C-VIC) strategy is developed, with the consideration of the difference in frequency regulation capability between wind power generators. The proposed control method can not only give full play to the frequency regulation capability of wind power generators, decrease the movements of the pitch angle control system but also bring some self-coordination capability to different wind power generators thus to avoid a secondary drop in system frequency. The simulations and experiments prove the proposed method to be effective and practicable.

• 한국지진공학회논문집
• /
• 제28권1호
• /
• pp.21-32
• /
• 2024

This study performed the seismic response analysis of an LNG storage tank supported by a disconnected piled raft foundation (DPRF) with a load transfer platform (LTP). For this purpose, a precise analytical model with simultaneous consideration of Fluid-Structure Interaction (FSI) and Soil-Structure Interaction (SSI) was used. The effect of the LTP characteristics (thickness, stiffness) of the DPRF system on the seismic response of the superstructure (inner and outer tanks) and piles was analyzed. The analytical results were compared with the response of the piled raft foundation (PRF) system. The following conclusions can be drawn from the numerical results: (1) The DPRF system has a smaller bending moment and axial force at the head of the pile than the PRF system, even if the thickness and stiffness of the LTP change; (2) The DPRF system has a slight stiffness of the LTP and the superstructure member force can increase with increasing thickness. This is because as the stiffness of the LTP decreases and the thickness increases, the natural frequency of the LTP becomes closer to the natural frequency of the superstructure, which may affect the response of the superstructure. Therefore, when applying the DPRF system, it is recommended that the sensitivity analysis of the seismic response to the thickness and stiffness of the LTP must be performed.

• 한국통신학회논문지
• /
• 제39A권6호
• /
• pp.333-342
• /
• 2014

본 논문은 OFDM 블록에 파일럿 심볼들이 빗 형태의 패턴에 따라 배치된 경우, 가상 부반송파를 가지는 OFDM 시스템의 channel frequency response (CFR)를 추정하는 여러 방식들을 서로 비교한다. 채널 임펄스 응답을 먼저 예측하는 것이 목적인 minimum mean square error (MMSE) 기반의 채널추정 방식과 누설현상의 억제가 목적인 MMSE 기반의 채널추정 방식이 지금까지 비교되지 않았기 때문에, 본 논문에서는 후자 방식과 전자 방식의 mean square error (MSE) 값들의 차이가 양수가 됨을 유도함으로써 전자 방식의 우수성을 논리적으로 증명한다. 아울러 본 논문에서는 파일럿 수의 변화가 MMSE 기반 채널추정 방식과 least-square (LS) 기반 채널 추정 방식의 성능에 미치는 영향을 조사한다. 컴퓨터 시뮬레이션을 통해 채널추정 방식들의 성능을 정량적으로 확인한다.

• Allergy, Asthma & Immunology Research
• /
• 제10권6호
• /
• pp.662-674
• /
• 2018

Purpose: Group 2 innate lymphoid cells (ILC2s) have been implicated in the pathogenesis of allergic disease. However, the effect of allergen-specific immunotherapy (AIT) on ILCs remains to be clarified. The aim of this study was to evaluate the levels of ILC subsets in allergic rhinitis (AR) patients in response to house dust mite (HDM)-specific immunotherapy. Methods: We enrolled 37 AR patients undergoing AIT (16 responders and 11 non-responders) for 2 years, 35 HDM AR patients and 28 healthy subjects. Peripheral blood mononuclear cells (PBMCs) were analyzed by flow cytometry to identify ILC subsets. Stimulation of ILC2s with recombinant allergen-specific protein was used to determine ILC2's activation (CD69 expression). Results: Responder AIT patients and healthy subjects had a decreased frequency of circulating ILC2s compared to non-responder AIT and AR patients. Conversely, ILC1s from responder AIT patients and healthy subjects showed increased frequency compared to non-responder AIT and AR patients. The frequency of ILC3s natural cytotoxicity receptor $(NCR)^+$ and $NCR^-$ in responder AIT patients was significantly lower compared to AR patients and healthy subjects. The ILC1: ILC2 proportion in responder AIT patients was similar to that of healthy subjects. PBMCs from patients who were responders to AIT had a significantly lower expression of the activation marker CD69 on ILC2s in response to allergen re-stimulation compared to AR patients, but no difference compared to non-responder AIT patients and healthy subjects. Conclusions: We propose that AIT might affect ILC responses. The activation of ILC2s was reduced in AR patients treated with AIT. Our results indicate that a relative ILC1/ILC2 skewed response is a possible key to successful AIT.

• 한국방재학회 논문집
• /
• 제11권1호
• /
• pp.7-13
• /
• 2011

지진에 대한 장대 교량의 정확한 반응 해석은 지진 방재에 있어서 중요한 역할을 한다. 본 논문은 비동기 다지지점 지진입력에 의한 교량의 반응을 진동수 영역방법과 시간 영역방법으로 해석하였으며 그 결과를 동기 입력 결과와 비교하였다. 시간영역방법에서는 선형모드 중첩 법으로 최대반응 값을 계산하였다. 진동수영역방법에서는 선형랜덤진동 이론을 사용하여 교량 성능에 영향을 미치는 모드와 다지지점 지진입력의 상호상관관계를 고려한 반응의 제곱평균근(RMS값)을 계산하였다. 교량 성능 반응 중, 변위 및 부재의 내력에 대한 시간 영역해석 결과와 진동수영역 해석 결과로부터 최대반응 값과 RMS값의 비로 정의된 최대반응 계수의 실용적인 값과 계산 방법을 요약하였다. 신뢰 있는 최대 반응계수가 있으면, 교량의 성능기반설계에서 구체적인 임의의 입력을 고려한 시간영역방법보다 결과의 일반성 및 수치적인 장점을 갖은 진동수영역방법이 더 효율적이다.

• 전기전자학회논문지
• /
• 제26권1호
• /
• pp.36-42
• /
• 2022

본 연구에서는 전기 신호 경로로서의 인체 채널에 대해 임펄스 응답 신호를 이용한 분석 결과를 제시한다. 최근, 인체 통신(human body communications)은 착용형 또는 임플란트형 센서 디바이스 간의 통신 방법으로 인체 영역 통신망(wireless body area networks)을 구성하는 효과적인 접근방법으로 제시되고 있다. 인체 통신 시스템 설계에 중요한 지침인 인체 채널 특성 제공을 위해, 자체 제작한 채널 응답측정장치를 사용하고 용량성 커플링(capacitive coupling) 특성에 적합한 실험환경을 구축하여 측정을 수행하고 그 분석한 결과를 제시한다. 측정 신호에 대한 신호처리 과정으로 임펄스 응답을 효과적으로 추출하여, 0 MHz에서 100 MHz 사이의 주파수 분석을 통해 평균 경로 손실 약 46.8 dB를 제시하고 주파수별 경로 손실 특성을 확인할 수 있다. 또한, 본 연구는 인체 통신 시스템의 수신기 신호 대 잡음비(signal-to-noise ratio) 예측을 위한 수신기 필터의 커패시터와 저항값 변화에 따른 전체 측정 주파수와 기저 대역 신호의 검출 성능 결정에 영향을 주는 3 MHz 이하 대역에서의 상대적인 잡음 전력을 제시하였다.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1995년도 봄 학술발표회 논문집
• /
• pp.136-143
• /
• 1995

The problem of the structural identification becomes important, particularly with relation to the rapid increase of the number of the damaged or deteriorated structures, such as highway bridges, buildings, and industrial facilities. This paper summarizes the recent studies related to those problems by the present authors. The system identfication methods are generally classified as the time domain and the frequency domain methods. As time doamin methods, the sequential algorithms such as the extended Kalman filter and the sequential prediction error method are studied. Several techniques for improving the convergences are incorporated. As frequency domain methods, a new frequency response function estimator is introduced. For damage estimation of existing structures, the modal perturbation and the sensitivity matrix methods are studied. From the example analysis, it has been found that the combined utilization of the measurement data for the static response and the dynamic (modal) properties are very effictive for the damage estimation.