• The Korean Journal of Ecology
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• 제21권5_2호
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• pp.491-499
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• 1998

An investigation was performed to establish the mathematical theories of a vibration for the plant growth and a wave distribution of a plant population on the boundary condition of a limiting factor in the environment. The mathematical theories of the plant growth vibration and wave distribution had been elucidated by the plant growth and the timber line on the middle slope of the west side of Mt. Paektu. The Betula ermaruii composes the timber line on about 2,060 m elevation of sea label, has a growth vibration on the ground surface and takes a wave distribution due to a boundary condition of alpine temperature gradient.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.629-633
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• 2006

We investigated a new longitudinal acceleration wave decomposition method in time domain. The proposed method separates up- and down-stream waves with an axial strain and axial acceleration measured at a single point on the transmission path. The advantages such as low computation load and easy implementation would be possible by developing time domain under the following assumptions; low frequency range, uniform cross sectional area and elastic wave propagation. We confirmed the feasibility and performance of the method through experiment using Split Hopkinson Pressure Bar (SHPB). The method can be effective in several applications, including active vibration control with wave view point, where real time wave decomposition is necessary.

• Smart Structures and Systems
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• 제23권5호
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• pp.405-420
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• 2019

In this study, vibration characteristics of offshore wind turbine tower (WTT) with gravity-based foundation (GBF) are identified from dynamic responses under wave-induced excitations. The following approaches are implemented to achieve the objective. Firstly, the operational modal analysis methods such as frequency domain decomposition (FDD) and stochastic subspace identification (SSI) are selected to estimate modal parameters from output-only dynamic responses. Secondly, a GBF WTT model composed of superstructure, substructure and foundation is simulated as a case study by using a structural analysis program, MIDAS FEA. Thirdly, wave pressures acting on the WTT structure are established by nonlinear regular waves which are simulated from a computational fluid software, Flow 3D. Wave-induced acceleration responses of the target structure are analyzed by applying the simulated wave pressures to the GBF WTT model. Finally, modal parameters such as natural frequencies and mode shapes are estimated from the output-only acceleration responses and compared with the results from free vibration analysis. The effect of wave height and period on modal parameter extraction is also investigated for the mode identification of the GBF WTT.

• Journal of Advanced Marine Engineering and Technology
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• 제37권6호
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• pp.596-602
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• 2013

기존의 진동에너지 하베스터는 한 주파수에서의 공진현상을 이용하여 에너지를 얻기 때문에 고정된 단일 주파수를 갖는 진동에너지로부터 전기에너지를 변환하는데 최적이지만 다양한 주파수를 포함하고 있는 파도와 같은 상하진동 에너지원으로부터 전기에너지를 얻는 데에는 한계가 있다. 본 논문에서는 이러한 단점을 해결하기위해 파도가 갖는 무한한 상하진동 에너지로부터 전기에너지를 얻는 광대역 진동에너지 하베스터를 연구하였다. 광대역 진동에너지 하베스터는 부양체와 진동에너지 하베스터가 각각 파도에너지가 갖는 중심주파수에서 공진이 발생되도록 구성되어있다. 그 결과 기존 공진을 이용한 진동에너지 하베스터는 한 주파수에서만 진동에너지를 전기에너지로 변환할 때 효율을 극대화할 수 있는 반면, 제안한 방법은 다양한 주파수를 포함하고 있는 파도에너지로부터 전기에너지로 변환할 때도 효율을 극대화 할 수 있는 장점을 가진다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.612-618
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• 2000

The underwater explosion which has the high energy brings about the shock wave and the pulsating gas bubble. In general, structural vibration from the shock wave is more serious than the pulsating gas bubble. This shock wave may damage the important fragile structures and equipment in ship. This paper demonstrates that the shock wave propagating the structure can be reduced by ER inserts. The wave transmission of ER inserted beam is theoretically derived using Mead & Markus model, and the theoretical results are composed with the finite element analysis results. To experimentally verify the ER insert, ER insert in an aluminum plate is made and two piezoceramic disks are used as transmitter and receiver. Details of the experiment are addressed.

• 한국지진공학회논문집
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• 제26권6호
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• pp.237-246
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• 2022

Based on the random-vibration-theory methodology, dynamic responses of nuclear facilities subjected to obliquely incidental and incoherent earthquake ground motions are calculated. The spectral power density functions of the 6-degree-of-freedom motions of a rigid foundation due to the incoherent ground motions are obtained with the local wave scattering and wave passage effects taken into consideration. The spectral power density function for the pseudo-acceleration of equipment installed on a structural floor is derived. The spectral acceleration of the equipment or the in-structure response spectrum is then estimated using the peak factors of random vibration. The approach is applied to nuclear power plant structures installed on half-spaces, and the reduction of high-frequency earthquake responses due to obliquely incident incoherent earthquake ground motions is examined. The influences of local wave scattering and wave passage effects are investigated for three half-spaces with different shear-wave velocities. When the shear-wave velocity is sufficiently large like hard rock, the local wave scattering significantly affects the reduction of the earthquake responses. In the cases of rock or soft rock, the earthquake responses of structures are further affected by the incident angles of seismic waves or the wave passage effects.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.661-666
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• 2000

Traveling wave on the structure can be generated by superposing two standing waves. Precise matching of the amplitudes and phase shift between two standing waves in time and space is the key to the success of generating a traveling wave. The principle of generating a traveling wave on the structure is utilized in the construction of linear and rotary type ultrasonic motors. This paper demonstrates experimentally generating a traveling wave on the simply supported beam.

• Structural Engineering and Mechanics
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• 제6권3호
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• pp.347-362
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• 1998

In this study an improved design method for the traditional A-type(or V-type) offshore template platform system was proposed to mitigate the vibration induced by the marine environmental loadings and the strong ground motions of earthquakes. A newly developed material model was combined into the structural system and then a nonlinear dynamic analysis in the time domain was carried out. The analysis was focused on the displacement and rotation induced by the input wave forces and ground motions, and the mitigation effect for these responses was evaluated when the viscoelastic damping devices were applied. The wave forces exerted on the offshore structures are based on Stokes fifth-order wave theory and Morison equation for small body. A step by step integration method was modified and used in the nonlinear analysis. It was found that the new design approach enhanced with viscoelastic dampers was efficient on the vibration mitigation for the structural system subjected to both the wave motion and the strong ground motion.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.508-513
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• 2000

Micro wave seeker detects micro wave signal reflecting from a object and modifies the angle of a antenna in the direction of a reflecting signal. Gimbal structure makes a motion in the direction of an elevation axis and an azimuth axis and change the direction of a missile toward a object. As before, Micro wave seeker is a important part of a missile. Especially, gimbal structure is designed to resist a external force generated by a strong propelling power. For that reason, it is essential to analyze a vibration feature of gimbal structure. In this paper, we analyze dynamic characteristics of a gimbal structure of a micro wave seeker. And we measure frequency response functions of a gimbal structure in order to investigate the effect of a pre-load on bearing.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.514-518
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• 2000

Micro wave seeker consists of a gimbal structure, a antenna and many RF parts. And Missile's propelling powers excite a gimbal structure, a antenna and many RF parts. Therefore, We must inquire into external forces to act on a micro wave seeker before everything. We must inquire into design parameters and then estimate dynamic characteristics of a gimbal structure with a finite element model to reflect part's characteristics for design for a gimbal structure in consideration of vibration features. In this paper, a gimbal structure of a micro wave seeker is modeled in finite element method and then updated by using the experimental modal data. Before we make a finite element model of a gimbal structure of a micro wave seeker, we make a finite element model of a sub-structure and compare with the experimental modal data.