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Effect of Parametric Excitation on Lateral Vibrations of Long, Slender Marine Structures
Han Il Park(박한일) 한국해양공학회 1993 韓國海洋工學會誌 Vol.7 No.1
본 연구에서는 장주형 해양구조물의 횡방향 진동에 대한 파라메트릭 가진의 효과를 고찰하였다. 먼저, 장주형 해양구조물의 횡방향 운동에 대한 4계 편미방지배방정식을 비선형 Mathieu 방정식으로 유도하였다. 비선형 Mathieu 방정식의 해를 구하여 장주형 해양구조물의 동적 반응 특성을 해석하였다. 유체 비선형 감쇠력은 불안정 조건하에 있는 파라메트릭 진동의 반응크기를 제한 하는데 중요한 역활을 한다. 파라메트릭 진동의 경우 가장 큰 반응크기는 Mathieu 안정차트의 첫번째 불안정 구간에서 일어난다. 반면에, 파라메트릭 진동과 강제진동의 결합 진동인 경우, 가장 큰 반응 크기는 두번째 불안정 구간에서 발생된다. 파라메트릭 가진으로 인한 장주형 해양구조물의 횡방향 운동은 동적조건에 따라 subharmonic, superharmonic 또는 chaotic 운동이 되기도 한다.
박한일(Han-Il Park),조효제(Hyo-Je Cho),정동호(Dong-Ho Jung) 한국해양공학회 1999 韓國海洋工學會誌 Vol.13 No.3(Ⅱ)
A deep-ocean mining riser pipe is subjected to floating vessel motion as well as environmental forces arising from currents and waves. The dynamic analysis is carried out for a deep-ocean mining riser pipe by using a finite element method. The vortex shedding which excites risers in a direction perpendicular to the flow and induces transverse response is considered. It is demonstrated that transverse displacements due to vortex shedding is greatly increased in lock-in regions. The result of this study is compared with other results having good agreements.
정동호,이용두,박한일,Jung Dong-Ho,Lee Yong-Doo,Park Han-Il 한국해양환경·에너지학회 2003 한국해양환경·에너지학회지 Vol.6 No.3
해저배관은 지반쇄굴로 인하여 일부분이 노출되어 자유경간이 형성될 수 있다. 자유경간이 형성되면 환경하중 및 와동유기진동에 의해서 안정성을 잃을 수 있다. 본 연구에서는 해저배관의 안정성을 위협하는 중요 요소인 자유경간의 정적 및 동적 경간을 결정하는 방법을 제시한다. 자유경간 해석에서는 해저배관에 작용하는 압축력 효과를 고려하였으며 토양의 종류에 따라 경계조건을 일반화시켰다. 자유경간 양단의 해저지반은 탄성기초로 간주하였으며, 이들 선형 및 회전 스프링으로 치환하여 경계조건을 일반화시켰다. 정적 및 동적 자유경간의 길이를 산정 할 수 있는 무차원화 된 곡선을 구하였다. 예제해석을 수행하여 그 적용방법을 소개하였다. 본 연구결과는 자유경간을 갖는 해저배관의 설계에 유용하게 적용될 수 있다. The free span of a subsea pipeline due to seabed scouring can result in structural failure by severe ocean environmental loads and vortex induced vibrations. This Paper examines the safety of subsea pipelines with free spans under axial compressive load. The variation of allowable lengths of static and dynamic free spans is examined for generalized boundary conditions. The free span is modelled as a beam with an elastic foundations and the boundary condition is replaced by linear and rotational springs at each end. The static and dynamic free span curves are obtained with a function of non-dimensional parameters. A case study is carried out to introduce the application method of the curve. The results of this study can be usefully applied for the design of subsea pipelines with a free span.
랜덤가진 하에 있는 ROV와 지지케이블의 수치해석 거동해석
권도영(DO-YOUNG KWON),박한일(HAN-IL PARK) 한국해양환경·에너지학회 2004 한국해양환경·에너지학회 학술대회논문집 Vol.2004 No.-
Ocean developments gradually move to deep-sea in the 21 century. A deep-sea unmanned underwater vehicle is one of important tools for ocean resource survey. A marine cable plays an important role for the safe operation and signal transmission of a deep-sea unmanned underwater vehicle. The first cable of a deep-sea unmanned underwater vehicle is excited by surface vessel motion and shows non-linear dynamic behaviors. A ROV launcher is also excited by the 1st cable motion. A numerical method is necessary for analysing the dynamic behaviour of the first marine cable and the ROV launcher. In this study, a numerical program is appled to a 6,000m long cable for a deep-sea unmanned underwater vehicle to show shows the dynamic behaviour of the cable and the ROV launcher under random excitations.
박춘군(Chun-Jun Piao),박한일(Han-Il Park) 한국해양공학회 1999 韓國海洋工學會誌 Vol.13 No.1
For offshore structures, dynamic analysis becomes increasingly important as water depth increases and structural configuration becomes more slender. In the case of dynamic analysis of frame structures, much computer time and high cost are required due to many degrees of freedom. In this paper, a new technique of permutating a segment of frame structure to a beam is developed, which is called here Beam Permutation Technique. The technique is based on definition of stiffness matrix of the beam which is obtained by defining the actions(or forces) required to obtain unit translation or rotation for each degree of freedom with all other degree of freedom restrained to zero displacement or rotation. In the technique, an assumption is made that relative positions of nodes in the ends of the segment are not variable. The technique can significantly reduce the degrees of freedom of frame structures and thus the computing time in dynamic analysis. The natural frequencies and static displacements of the permutated beam are obtained and compared to those of ANSYS with a good agreement.
비선형 최소제곱법을 이용한 점탄성 감쇠를 갖는 원통셸의 실험진동해석
민천홍(CHEON-HONG MIN),박한일(HAN-IL PARK),배수룡(SOO-RYONG BAE) 한국해양공학회 2008 韓國海洋工學會誌 Vol.22 No.3
It is a recent trend for advanced ships and submarines to incorporate composite structureswith viscoelastically damping material. Much research has been done on curve-fitting techniquesto identify vibration characteristic parameters such as natural frequencies, modal damping ratios, and mode shapes of the composite structure. In this study, an advanced technique for accurately determining vibration characteristic of a circular cylindrical shell-attached viscoelastically damping material is used, based on a multi-degree of freedom (MDOF) curve-fitting method. First, an initial value is obtained by using a linear least square method. Next,sung the initial value, the exact model parameters of the composite circular cylindrical shell are obtained by using a nonlinear least square method. Results show computation time is greatly decreased and accurate results are obtained by the MDOF curve-fitting method.