• 한국해양공학회지
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• 제35권5호
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• pp.347-359
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• 2021

This study aims to evaluate the dynamic responses of the jacket-type offshore wind turbine using FAST software (Fatigue, Aerodynamics, Structures, and Turbulence). A systematic series of simulation cases of a 5 MW jacket-type offshore wind turbine, including wind-only, wave-only, wind & wave load cases are conducted. The dynamic responses of the wind turbine structure are obtained, including the structure displacement, rotor speed, thrust force, nacelle acceleration, bending moment at the tower bottom, and shear force on the jacket leg. The calculated time-domain results are transformed to frequency domain results using FFT and the environmental load with more impact on each dynamic response is identified. It is confirmed that the dynamic displacements of the wind turbine are dominant in the wave frequency under the incident wave alone condition, and the rotor thrust, nacelle acceleration, and bending moment at the bottom of the tower exhibit high responses in the natural frequency band of the wind turbine. In the wind only condition, all responses except the vertical displacement of the wind turbine are dominant at three times the rotor rotation frequency (considering the number of blades) generated by the wind. In a combined external force with wind and waves, it was observed that the horizontal displacement is dominant by the wind load. Additionally, the bending moment on the tower base is highly affected by the wind. The shear force of the jacket leg is basically influenced by the wave loads, but it can be affected by both the wind and wave loads especially under the turbulent wind and irregular wave conditions.

• International Journal of Advanced Culture Technology
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• 제8권2호
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• pp.159-164
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• 2020

The response analysis of frame structure with open section beams considering warping conditions and short duration load have been performed. When a beam of frame structure is subjected under torsional moment, the cross section will deform a warping as well as twist. For some thin-walled sections warping will be large, and accompanying warping restraint will induce axial and shear stresses and reduce the twist of beam which stiffens the beam in torsion. Because of impact or blast loads, the wave propagation effects become increasingly important as load duration decreases. This paper presents that a warping restraint in finite element model effects the behavior of beam deformation, dynamic mode shape and response analysis. The computer modelling of frame is discussed in linear beam element model and linear thin shell element model, also presents a correlation between computer predicted and actual experimental results for static deflection, natural frequencies and mode shapes of frame. A method to estimate the number of normal modes that are important is discussed.

• 한국생산제조학회지
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• 제23권5호
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• pp.471-477
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• 2014

The purpose of this study was to predict the load effect on a damper installed at a nuclear power plant building after a tsunami using a volume of fluid (VOF) numerical analysis method. The wave height was determined by a sine wave function and the tsunami condition was estimated by the wave length. Also, using computational fluid dynamics (CFD), the maximum damper load was set as a boundary condition for the structural analysis that verified how stress and deformation affect the damper. As a result, such simulations estimated the highest stress distribution for a wave length of 350 m with a maximum stress present at the cross point of stiffness installed at the rear end of the damper. The total deformation was approximately 32 mm at the center of damper.

• 전기학회논문지
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• 제60권8호
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• pp.1566-1571
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• 2011

The objective of this paper is to present a quantitative analysis leading to the assessment of optimum terminating impedances in the design of active frequency multipliers. A brief analysis of the basic principal of the GaAs FET frequency multiplier is presented. The analysis is outlined in bias optimization and drive power determination. Utilizing the equivalent circuit model of GaAs FET, we have simulated the optimized load impedance for the maximum output of the active frequency multipliers. The C-class and reverse C-class frequency doublers have been fabricated and the load impedances have been measured. The experimental results are in good agreement with the estimated results in the simulation with the accuracy of 90%.

• 한국해안·해양공학회논문집
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• 제25권1호
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• pp.20-27
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• 2013

태풍에 의해 발생된 파랑하중에 의해 방파제, 안벽 등과 같은 해안구조물 하부의 해저지반 침하가 발생될 수 있다. 만약 해저지반이 모래인 경우, 잔류과잉간극수압발생과 반복적인 파랑하중에 의해 해저지반의 침하현상이 더 발생될 확률이 높아질 것이다. 그러나 대부분의 해안구조물은 설계에서 파랑하중을 정적상태의 등분포하중으로 구조물에만 작용하는 것으로 가정하고 있지만 실제로는 동적인 파랑하중이 구조물과 해저지반에 동시에 작용한다. 따라서 본 연구에서는 시간에 따른 실제파압을 고려하고, 구조물뿐만 아니라 해저지반에도 작용하는 것으로 고려하였다. 수치해석 결과 파랑하중이 구조물과 해저지반에 큰 영향을 미친 것으로 나타났다. 시간에 따른 해저지반의 변형거동이 해석되었으며 해저지반에서 유효응력의 변화와 유효응력경로의 변화를 분명하게 확인할 수 있었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.184.2-184.2
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• 2010

With growing of wind turbine industry, offshore wind turbine system is getting more attention in recent years. Foundation of the offshore wind turbine plays a key role in stability of whole system. In this work, 5MW NREL reference wind turbine with rated speed of 11.4m/s is used for load calculation. Wind loads and wave loads are evaluated using GH-Bladed (Garard Hassan) and FAST (NREL). Additionally, FE simulation is carried out to investigate the wave effect on the support structure. Meanwhile, this work is trying to systematize and optimize load cases simulation for foundation of wind turbine system.

• Ocean Systems Engineering
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• 제13권4호
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• pp.349-365
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• 2023

Targeting a floating wave and offshore wind hybrid power generation system (FWWHybrid) designed in the Republic of Korea, this study examines the impact of the interaction, with multiple wave energy converters (WECs) placed on the platform, on platform motion. To investigate how the motion of WECs affects the behavior of the FWWHybrid platform, it was numerically compared with a scenario involving a 'single-body' system, where multiple WECs are constrained to the platform. In the case of FWWHybrid, because the platform and multiple WECs move in response to waves simultaneously as a 'multi-body' system, hydrodynamic interactions between these entities come into play. Additionally, the power take-off (PTO) mechanism between the platform and individual WECs is introduced for power production. First, the hydrostatic/dynamic coefficients required for numerical analysis were calculated in the frequency domain and then used in the time domain analysis. These simulations are performed using the extended HARP/CHARM3D code developed from previous studies. By conducting regular wave simulations, the response amplitude operator (RAO) for the platform of both single-body and multi-body scenarios was derived and subsequently compared. Next, to ascertain the difference in response in the real sea environment, this study also includes an analysis of irregular waves. As the floating body maintains its position through connection to a catenary mooring line, the impact of the slowly varying wave drift load cannot be disregarded. To assess the influence of the 2^nd-order wave exciting load, irregular wave simulations were conducted, dividing them into cases where it was not considered and cases where it was included. The analysis of multi-degree-of-freedom behavior confirmed that the action of multiple WECs had a substantial impact on the platform's response.

• Geomechanics and Engineering
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• 제19권3호
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• pp.241-254
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• 2019

A finite element approach is presented to examine ground vibration characteristics under various moving loads in a homogeneous half-space. Four loading modes including single load, double load, four-load, and twenty-load were simulated in a finite element analysis to observe their influence on ground vibrations. Four load moving speeds of 60, 80, 100, and 120 m/s were adopted to investigate the influence of train speed to the ground vibrations. The results demonstrated that the loading mode in a finite element analysis is reliable for train-induced vibration simulations. Additionally, a three-dimensional finite element model (3D FEM) was developed to investigate the dynamic responses of a track-ballast-embankment-ground system subjected to moving loads induced by high-speed trains. Results showed that vibration attenuations and breaks exist in the simulated wave fronts transiting through different medium materials. These tendencies are a result of the difference in the Rayleigh wave speeds of the medium materials relative to the speed of the moving train. The vibration waves induced by train loading were greatly influenced by the weakening effect of sloping surfaces on the ballast and embankment. Moreover, these tendencies were significant when the vibration waves are at medium and high frequency levels. The vibration waves reflected by the sloping surface were trapped and dissipated within the track-ballast-embankment-ground system. Thus, the vibration amplitude outside the embankment was significantly reduced.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.856-857
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• 2008

Wave power generation as an environmentally -friendly energy has received the attention. In this paper, therefore, the tubular type Permanent Magnet Linear Synchronous Generator (PMLSG) is proposed for wave power generation. The characteristics of tubular type PMLSG are investigated by analysis using a Finite Element Analysis (FEA). Moreover, the operating performance of generator under no-load and load with variable resistance is examined. And Taguchi method is applied for considering tolerance in manufacture. The results of FEA show that proposed tubular type PMLSG is a useful solution for small-scale wave power generation.

• 대한조선학회 특별논문집
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• 대한조선학회 2005년도 특별논문집
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• pp.31-37
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• 2005

An attempt to improve the speed performance through the minimizing in wave resistance has been done by an application of gooseneck and no bulb type to bulbous bow for the DSME 78,500 Class LPG Carrier on the basis of the CFD calculation and comparatives model tests. The hydrodynamic characteristics according to the variation of the shape of Cp-curve, design load water line, frame line and bulbous bow that have an important effect on the wave resistance has been evaluated/calculated by ship-flow code. A wide variety in hull variation have been tried to have a good hull form with three types of fore-body hull forms mainly classified by the shape of bulbous bow. The speed performances for the three final hull forms with different bulbous bows have been evaluated through the model tests.