• 한국해안·해양공학회논문집
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• 제26권5호
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• pp.300-313
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• 2014

파-지반의 상호작용 해석에 지금까지는 대부분 무한두께를 갖는 해저지반 상의 진행파와 무한두께 혹은 유한두께의 해저지반 상에서 완전중복파에 대해서만 해석해가 제안되어 있다. 본 연구에서는 임의반사율의 부분중복파동장에 선형파 이론과 유한두께를 갖는 해저지반에 Biot(1941) 3차원 압밀이론 및 지반탄성론에 기초한 유효응력 개념을 각각 적용하여 지반 내 동적응답에 관한 해석해를 새롭게 유도하며, 이에 수심과 반사율만을 변화시킴으로서 기존의 해석해가 간단히 얻어지기 때문에 그의 적용성이 보다 넓다. 본 해석해의 타당성은 무한지반 상의 진행파동장 및 완전중복파동장에 대한 Yamamoto et al.(1978) 및 Tsai & Lee(1994)의 해석해와 비교 검토로부터 검증된다. 또한, 본문에서는 유한깊이를 갖는 해저지반 상의 진행파동장, 완전중복파동장 및 임의반사율의 부분중복파동장에 대해 수심과 주기의 변화에 따른 본 해석해의 변화특성을 면밀히 검토한다. 이로부터 유한깊이의 지반은 무한두께의 경우와는 매우 상이한 지반응답(간극수압, 전단응력, 수평 및 연직 유효응력)을 나타내고, 반사율의 함수인 부분중복파동장에서 지반응답은 완전중복파동장에서의 값보다 일반적으로 작은 값을 나타낸다는 것을 확인할 수 있었다.

• Journal of the Optical Society of Korea
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• 제5권3호
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• pp.76-82
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• 2001

The optical response for traveling-wave Mach-Zehnder modulators without-with phased reversal is successfully derived in more concise and succinct form than any other equations before. The obtained equation is applied to a bandpass traveling-wave modulator with 3-section phase reversal and is confirmed to be in reasonable agreement with the experimental data.

• Earthquakes and Structures
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• 제22권4호
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• pp.373-386
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• 2022

The development of performance-based design methodologies requires a reasonable definition of a displacement-response spectrum. Although ground motions are known to be significantly affected by the resonant-like amplification behavior caused by multiple wave reflections within the surface soil, such a soil-resonance effect is seldom explicitly considered in current-displacement spectral models. In this study, an analytical approach is developed for the construction of displacement-response spectra by considering the soil-resonance effect. For this purpose, a simple and rational equation is proposed for the response spectral ratio at the site fundamental period (SRTg) to represent the soil-resonance effect based on wave multiple reflection theory. In addition, a bilinear model is adopted to construct the soil displacement-response spectra. The proposed model is verified by comparing its results with those obtained from actual observations and SHAKE analyses. The results show that the proposed model can lead to very good estimations of SRTg for harmonic incident seismic waves and lead to reasonable estimations of SRTg and soil displacement-response spectra for earthquakes with a relatively large magnitude, which are generally considered for seismic design, particularly in high-seismicity regions.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2001년도 Proceeding of KIN-CIN Joint Symposium 2001 on Satellite Navigation/AIS, lntelligence , Computer Based Marine Simulation System and VDR
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• pp.153-168
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• 2001

In the country where the population concentrates in the metropolis with the narrow land, development of th ocean space is necessary. Recently, mega-float offshore structure is studied as one of the effective utilization of the ocean space. And very large floating structure are now being considered for various applications such as floating airports, offshore cities and so on. This very large structure is relatively flexible compared with real floating structures like large ships. when we estimate dynamic responses of these structures in waves, the elastic deformation is important, because vertical dimension is small compared with horizontal. And it is necessary to examine the effect of ocean wave eternal force received from the natural environment. In this study, the mat-type large floating structure is made to be analytical model. And the analysis of the dynamic response as it receives regular wave is studied. The finite element method is used in the analysis of structure part of this model. And the analysis is carried out using the boundary element method in the fluid part. In order to know the characteristics of the dynamic response of the large floating structures, effects of wavelength, bending rigidity of the structure, water depth, and wave direction on dynamic response of the floating structure are studied by use of numerical calculation.

• 한국항해항만학회지
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• 제37권1호
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• pp.63-69
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• 2013

Since most merchant vessels are mainly influenced by the added resistance in an actual sea, they could be navigated more efficiently if this added resistance could be precisely predicted and then effectively reduced. In this paper, we have computed the effective horsepower based on the resistance performance in still water and then calculated the added resistance in regular wave in order to estimate a ship's propulsion performance on a voyage. Firstly, we have performed experiments using a model of KCS in a circulating water channel to estimate the flow characteristics around a container ship and the ship's resistance in still water. Then we have calculated the motion response function in regular wave as well as the values for the increase in resistance, and evaluated the ship's motion performance in waves according to the calculated response function. It was found that the resistance in waves increased because the ship's motion response value became larger as the ship's speed increased in the case of head sea. The effect of the added resistance could be reduced by maneuvering the ship to the encounter angle of $120^{\circ}$ in areas of long wavelengths and to head sea in areas of short wavelengths.

• Earthquakes and Structures
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• 제12권2호
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• pp.153-163
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• 2017

The underlying goal of the present paper is to investigate soil and structural uncertainties on impedance functions and structural response of soil-shallow foundation-structure (SSFS) system using Monte Carlo simulations. The impedance functions of a rigid massless circular foundation resting on the surface of a random soil layer underlain by a homogeneous half-space are obtained using 1-D wave propagation in cones with reflection and refraction occurring at the layer-basement interface and free surface. Firstly, two distribution functions (lognormal and gamma) were used to generate random numbers of soil parameters (layer's thickness and shear wave velocity) for both horizontal and rocking modes of vibration with coefficients of variation ranging between 5 and 20%, for each distribution and each parameter. Secondly, the influence of uncertainties of soil parameters (layer's thickness, and shear wave velocity), as well as structural parameters (height of the superstructure, and radius of the foundation) on the response of the coupled system using lognormal distribution was investigated. This study illustrated that uncertainties on soil and structure properties, especially shear wave velocity and thickness of the layer, height of the structure and the foundation radius significantly affect the impedance functions, and in same time the response of the coupled system.

• 한국항해학회지
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• 제24권1호
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• pp.85-95
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• 2000

In the country where the population concentrates in the metropolis with the narrow land, development of the ocean space is necessary. Recently, mega-float offshore structure has been studied as one of the effective utilization of the ocean space. And very large floating structures are now being considered for various applications such as floating airports, offshore cities and so on. This very large structure is relatively flexible compared with real floating structures like large ships. when we estimate dynamic responses of these structures in waves, the elastic deformation is important, because vertical dimension is small compared with horizontal. And it is necessary to examine the effect of ocean wave external force received from the natural environment. In this study, the mat-type large floating structure is made to be analytical model. And the analysis of the dynamic response as it receives regular wave is studied. The finite element method is used in the analysis of structural section of this model. And the analysis is carried out using the boundary element method in the fluid division. The validity of analysis method is verified in comparison with the experimental result in the Japan Ministry of Transport Ship Research Institution. In order to know the characteristics of the dynamic response of the large floating structures, effects of wavelength, bending rigidity of the structure, water depth, and wave direction on dynamic response of the floating structure are studied by use of numerical calculation.

• Geomechanics and Engineering
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• 제28권1호
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• pp.25-33
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• 2022

The energy transferred on drill rods by dynamic impact mainly determines the penetration depth for in-situ tests. In this study, the dynamic response and transferred energy of drill rods are determined from the frequency of the stress waves. AW-type drill rods of lengths 1 to 3 m are prepared, and strain gauges and an accelerometer are installed at the head and tip of the connected rods. The drill rods are hung on strings, allowing free vibration, and then impacted by a pendulum hammer with fixed potential energy. Increasing the rod length L increases the wave roundtrip time (2L/c, where c is the wave velocity), and hence the transferred energy at the rod head. At the rod tip, the first velocity peak is higher than the first force peak because a large and tensile stress wave is reflected, and the transferred energy converges to zero. The resonant frequency increases with rod length in the waveforms measured by the strain gauges, and fluctuates in the waveforms measured by the accelerometer. In addition, the dynamic response and transferred energy are perturbed when the cutoff frequency is lower than 2 kHz. This study implies that the resonant frequency should be considered for the interpretation of transferred energy on drill rods.

• Ocean Systems Engineering
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• 제4권4호
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• pp.327-342
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• 2014

The tension leg platform (TLP) is one of the compliant structures which are generally used for deep water oil exploration. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to the vertical degrees of freedom, it is stiff and resembles a fixed structure and is not allowed to float freely. In the current study, a numerical study for square TLP using modified Morison equation was carried out in the time domain with water particle kinematics using Airy's linear wave theory to investigate the effect of changing the tether tension force on the stiffness matrix of TLP's, the dynamic behavior of TLP's; and on the fatigue stresses in the cables. The effect was investigated for different parameters of the hydrodynamic forces such as wave periods, and wave heights. The numerical study takes into consideration the effect of coupling between various degrees of freedom. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables. Nonlinear equation was solved using Newmark's beta integration method. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e., 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether tension force, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations that is significantly dependent on wave height, and that special attention should be given to tethers fatigue because of their high tensile static and dynamic stress.

• 대한의용생체공학회:의공학회지
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• 제20권3호
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• pp.307-314
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• 1999

M-wave 는 신경전도 연구에 있어서 후기반응 현상 중 직접적인 반응으로, 반응 후 일정시간내에 정보가 존재하는 단발 반응의 특성을 가지고 있다. 이러한 M-wave 는 신경계통의 질환을 진단하기 위한 유용한 요소이며, 따라서 M-wave 의 형태 및 시간에 관한 정보가 간단히 표현될 수 있다면 신경질환 연구에 많은 도움이 될 것이다. 따라서 본 연구에서는 Ar 모델링 방법이 이러한 M-wave 의 정보 압축에 있어서 효과적임을 증명하였다. 이로 인해 먼저 실제로 측정된 M-wave 신호에서 Ar 파라메터를 추정하였으며, 추정된 파라메터를 가지고 근사화한 곡선과 최근의 M-wave의 정보압축에 관한 연구인 Hermite 변환을 이용한 방법에 따른 근사화 곡선을 비교하였다. 제안된 방법의 구체적인 검증을 위해 실신호와 근사화 곡선의 정규화 평균자승오차(NMSE)를 구하여 비교하였다. 결론적으로 M-wave 의 정보를 압축하는데 있어 Hermite 변환은 30개의 파라메터가 필요한 반면, 본 연구에서 제시한 AR 모델링방법은 3개의 파라메터만 가지고도 효과적으로 M-wave 의 특징을 압축할 수 있음을 보였다.