• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.6
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• pp.45-54
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• 2019

In this study, we analyze the rattle noise of a power takeoff (PTO) driveline and develop a PTO driveline resonance model. We measured the rattle noise of the PTO driveline on the output shaft and, by analyzing the rattle noise in the time domain, we determine that the engine expansion stroke period matches the sound pressure of rattle noise. This finding helped us demonstrate that the rattle noise is caused by the collision between the PTO driving gear and the gear driven by the engine expansion stroke; the torsional vibration caused by this collision is affected by the angular velocity fluctuation of the PTO drive shaft. By measuring the angular velocity of the PTO drive shaft, we confirm that the angular velocity fluctuation of the engine flywheel tends to excessively amplify the PTO drive shaft angular velocity fluctuation. We conclude that the resonance, which occurs when the operating frequency of the engine is close to the natural frequency of the tractor power transmission system, causes the excessive angular velocity fluctuation of the PTO drive shaft. We performed a modal analysis of the PTO driveline resonance and, using the characteristic equation, we show that the resonance occurs when the engine rotation speed is close to 850 rpm, which matches the natural frequency of the PTO driveline.

• Journal of Software Assessment and Valuation
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• v.15 no.1
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• pp.71-78
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• 2019

Lasers for optical broadband communication systems should have excellent frequency selectivity and modal stability. DFB lasers have low lasing frequency shift during high speed current modulation. In this paper, we have developed a simulation software and analysed beam profiles of a lasing mode in longitudinal direction of an 1.55um DFB laser with two mirrors and without anti-reflection coatings, that have both an index- and gain-gratings. As the phases of the index and gain gratings on the mirror faces are varied, the beam profiles |R(z)| and |S(z)| of the lasing mode with the emitted power ratio P_l/p_r are analysed and examined. In order to reduce the threshold current of a lasing mode and enhance the frequency stability, κL should be greater than 8, regardless of the grating phases on the mirror faces.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.8
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• pp.692-700
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• 2014

In this work, satellite FE (finite element) model updating for the prediction of the effect of micro-vibration is described. In the case of satellites launched in low earth orbit, high agility and more mission accomplishments are required by the customer in order to procure many images from satellites. To achieve the goal, many mechanisms, including high capacity wheels and antennas with multi-axis gimbals have been widely adopted, but they become a source of micro-vibration which could significantly deteriorate the quality of images. To investigate the effect due to the micro-vibration in orbit on the ground, a prediction is conducted through an integrated model coupling the measured jitter sources with FE (finite element) model. Before prediction, the FE model is updated to match simulation results with the modal survey test. Subsequently, the quality of FE model is evaluated in terms of frequency deviation error, the resemblance of mode shapes and FRFs (frequency response functions) between test and analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.1
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• pp.123-132
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• 1985

The flexibility of base material gives considerable influences on seismic responses of a structure. The effects of relative stiffness between super-structure and base material on dynamic soil-structure interaction are evaluated by parametric studies. Two 5-story buildings are used for the study; one is shearwall structure with relatively higher fundamental frequency and the other is frame structure with relatively lower fundamental frequency. The structures are modeled as beam-sticks coupled with springs and dashpots representing the base material. Dynamic equilibrium equations of the soil-structure interaction system are sloved by mode superposition method using Rosset modal damping values. Soil-structure interaction effect is found to be major concern in seismic analysis of shearwall structure in most cases while it seldom becomes engineering problem in frame-type structure. It is also found that seismic responses at lower elevation of the super-structure are amplified though they decrease at higher elevation as soil-structure interaction effects of the system increase.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.270-278
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• 2020

In this paper, sound transmission of Micro-Perforated Plates (MPPs) installed in an impedance tube with a circular cross-section is described using an analytic method. Vibration of the plates is expressed in terms of an infinite series of modal functions, where modal function in the radial direction is given by the Bessel function. Under the plane wave assumption, a low frequency approximation is derived, and a formula for the sound transmission coefficient of multi-layered MPPs is presented using the transfer matrix method. The Sound Transmission Losses (STLs) of single and double MPPs are computed using the proposed method and compared with those done by the Finite Element Method (FEM), which shows an excellent agreement. As the perforation increases, the STL is degraded, since the STL becomes dominated by the perforation ratio rather than by vibration of the plate. The STL shows dips at natural frequencies as well as at the mass-spring-mass resonance frequency. The proposed model for the STL prediction in this study can be applied to an arbitrary number of MPPs, where each MPP may or may not have a perforation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.119-125
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• 2020

Research on high-attenuation concrete for the vibration reduction performance by mixing epoxy-based synthetic resins and aggregates is actively being conducted. The curing time of high-attenuation concrete is very short because water is not used, and the physical and dynamic properties are very excellent. therefore, it is expected to be widely used in building structures requiring reduction of interior-floor noise and vibration. Furthermore, A way to expand the applicability of the high-damping concrete mixed with polymer in the field of reinforcement material have been variously studied. In order to replace polymer concrete with ordirnary concrete and existing anti-vibration reinforcement material, it is necessary to review overall vibration reduction performance considering physical properties, dynamic properties, productivity and field applicability. In this study, the physical and dynamic properties of polymer concrete by epoxy mixing ratio compared with ordirnary concrete. As a result, the elastic modulus was similar. On the other hand, polymer concrete for the compressive, tensile, and flexural strengths was quite more excellent. In particular, the measured tensile strength of polymer concrete was 4-10 times higher than that of ordirnary concrete. it was a big difference, and the frequency response function and damping ratio was studied through modal test and finite element analysis model. The dynamic stiffness of polymer concrete was 20% greater than that of ordirnary concrete, and the damping ratio of polymer concrete was approximately 3 times more than that of ordirnary concrete.

• Structural Engineering and Mechanics
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• v.75 no.4
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• pp.507-518
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• 2020

With the rapid development of rail transit, rail transit noise needs to be paid more and more attention. In order to accurately and effectively analyze the characteristics of low-frequency noise, a prediction model of vibration of box girder was established based on the hybrid FE-SEA method. When the train speed is 140 km/h, 200 km/h and 250 km/h, the vibration and noise of the box girder induced by the vertical wheel-rail interaction in the frequency range of 20-500 Hz are analyzed. Detailed analysis of the energy level, sound pressure contribution, modal analysis and vibration loss power of each slab at the operating speed of 140 km /h. The results show that: (1) When the train runs at a speed of 140km/h, the roof contributes more to the sound pressure at the far sound field point. Analyzing the frequency range from 20 to 500 Hz: The top plate plays a very important role in controlling sound pressure, contributing up to 70% of the sound pressure at peak frequencies. (2) When the train is traveling at various speeds, the maximum amplitude of structural vibration and noise generated by the viaduct occurs at 50 Hz. The vibration acceleration of the box beam at the far field point and near field point is mainly concentrated in the frequency range of 31.5-100 Hz, which is consistent with the dominant frequency band of wheel-rail force. Therefore, the main frequency of reducing the vibration and noise of the box beam is 31.5-100 Hz. (3) The vibration energy level and sound pressure level of the box bridge at different speeds are basically the same. The laws of vibration energy and sound pressure follow the rules below: web

• Journal of Software Assessment and Valuation
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• v.16 no.1
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• pp.55-63
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• 2020

Lasers for optical broadband communication systems should have excellent frequency selectivity and modal stability. DFB lasers have low lasing frequency shift during high speed current modulation. In this paper, when a refractive index grating and a gain grating are simultaneously present in a DFB laser having a wavelength of 1.55 ㎛, the dielectric film is coated so that reflection does not occur on the right mirror surface, so that ρ_r=0. For the first mode, which requires a minimum gain at the threshold, the beam distribution of the oscillation mode in the longitudinal direction and the radiated power ratio P_l/P_r were analyzed and compared for the cases of the phase of ρ_l=π and π/2. If the phase of ρ_l=π, in order to obtain a low threshold current and high frequency stability, κL should be greater than 8. In the case of the phase of ρ_l=π/2, for low threshold current, κL is necessary to be 1.0, where the oscillation frequency coincides with the lattice frequency. DFB lasers with an anti-reflection coated mirror have excellent mode selectivity than 1.55um DFB lasers with two mirror facets

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.574-577
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• 2007

본 논문에서는 실 시공 중인 PSC 교량에 대하여 풍하중에 의한 상시 진동 계측 자료을 기반으로, 교량의 동특성(고유진동수, 모드형상)을 추정하였으며, 이를 바탕으로 대상 교량의 탄성계수를 추정하여 정적 계측을 통한 탄성계수 결과와 비교하였다. 본 논문에서 사용한 동특성 추정 기법은, 대표적인 주파수 영역 해석 방법인 Frequency Domain Decomposition(FDD) 방법과 시간영역 해석 방법인 Stochastic Subspace Identification(SSI) 방법을 이용하였다. 탄성계수 추정은 유한요소모델과 계측 결과를 이용하여 두 개의 결과 차이가 수렴하도록 하는 반복 계산을 통해 탄성계수를 추정하였다. 우선, 탄성계수 추정 기법의 검증을 위해, 수치 해석을 통하여 그 기법을 검증하였으며, 해석 결과 정확한 탄성계수값을 추정하였으며, 이를 통해 본 논문에서 적용한 탄성계수 추정법에 대한 신뢰도를 확인하였다. 이를 바탕으로 사용된 추정 기법을 실 교량에 적용하기 위해 실제 상시 진동 계측 값을 바탕으로 실교량의 동특성 및 탄성계수를 추정하였다. FDD 및 SSI 기법을 통한 모드 해석 결과, 두 기법 모두 유사한 결과를 나타내어 FDD 및 SSI 두 방법에 대한 결과의 신뢰도를 확인 할 수 있었다. 추정 탄성계수 값은 거더 단면내 설치한 응력계 및 변형률계를 통한 계측 결과값의 범위 내에 있음을 확인하였다. 따라서 본 논문에서 적용한 교량의 상시 진동 데이터를 바탕으로 한동특성 및 탄성계수 추정법이 구조물의 대략적인 탄성계수 및 이에 따른 구조물의 전체적인 건전도를 파악하는데 도움이 되리라 생각된다.

• Smart Structures and Systems
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• v.14 no.3
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• pp.327-345
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• 2014

This paper presents a composite control strategy for the active suppression of vibration due to the unknown disturbances, such as external excitation, harmonic effects and control spillover, as well as high-frequency accelerometer measurement noise in the all-clamped stiffened plate. The proposed composite control action based on the modal approach, consists of two contributions including feedback part and feedforward part. The feedback part is the well-known PID controller, which is widely used to increase the structure damping and improve its dynamic performance close to the resonance frequencies. In order to get better performance for vibration suppression, the weight matrixes is optimized by chaos sequence. Then an improved disturbance observer (IDOB) as the feedforward compensation part is developed to enhance the vibration suppression performance of PID under various disturbances and uncertainties. The proposed IDOB can simultaneously estimate the various disturbances dynamically as well as measurement noise acting on the system and suppress them by feedforward compensation design. A rigorous analysis is also given to show why the IDOB can effectively suppress the unknown disturbances and measurement noise. In order to verify the proposed composite control algorithm (IDOB-PID), the dSPACE real-time simulation platform is used and an experimental platform for the all-clamped stiffened plate active vibration control system is set up. The experimental results demonstrate the effectiveness, practicality and strong anti-disturbances ability of the proposed control strategy.