• Title/Summary/Keyword: eigenfunction

Search Result 169, Processing Time 0.026 seconds

Experimental Study on the Hydroelastic Response of a Pontoon Type Structure with Nonuniform Mass and Stiffness (불균일 강성을 갖는 폰툰형 구조물의 유탄성 응답 특성에 관한 실험 연구)

  • Cho, Seok-Kyu;Hong, Sa-Young;Kim, Jin-Ha
    • Journal of the Society of Naval Architects of Korea
    • /
    • v.41 no.5
    • /
    • pp.34-40
    • /
    • 2004
  • Very Large Floating Structure(VLFS) is regarded as one of promising candidates for the future utilization of ocean space. VLFS has the merits of small environmental effect. short construction term, easiness for extension and removal. It is well known that hydroelastic response is one of major design concerns of such a huge structure. Most of studies on the hydroelastic analysis of VLFS assumed uniform mass and bending stiffness. In case of a floating hotel where noticeable change of mass and stiffness at the hotel part is expected. it is necessary to investigate the effect of nonuniform mass and bending stiffness on the hydroelastic response. A model test of a pontoon type VLFS with nonuniform bending stiffness carried out for performance evaluation of a floating marina-hotel-convention center is described in this paper. Through investigation of model test results and comparison with numerical analysis using eigenfunction method, effect of the variation of bending stiffness is discussed.

Scattering Wave Spectrum by a Pile Breakwater in Directional Irregular Waves (다방향 불규칙 파랑중 파일 방파제에 의한 산란파 스펙트럼)

  • Cho, Il-Hyoung
    • Journal of Korean Society of Coastal and Ocean Engineers
    • /
    • v.19 no.6
    • /
    • pp.586-595
    • /
    • 2007
  • The analytic solution of wave scattering of monochromatic waves on a pile breakwater by an eigenfunction expansion method is extended to the case of directional irregular waves. The scattering wave spectrum and the force spectrum can be expressed from the reflection coefficient, transmission coefficient and the wave forces obtained from changing frequencies and incident angles in monochromatic waves. By numerical integration of 2-dimensional spectrum which is function of frequencies and incident angles, the representative values for the scattered waves and wave forces are obtained and the dependence of the transmission coefficients and wave forces on the directional distribution function, the principal wave direction, the submergence depth, and porosity is analyzed.

Wave Structure Interaction by Installation of New Circular Caissons on Old Circular Caisson Breakwater (기존 원형케이슨방파제에 신규 원형케이슨 추가설치에 따른 파와 구조물간의 상호작용 영향 평가)

  • Park, Min Su
    • Journal of Korean Society of Coastal and Ocean Engineers
    • /
    • v.32 no.5
    • /
    • pp.307-321
    • /
    • 2020
  • The design and the construction are carried out by installation of new caissons on the back or the front of old caissons to increase the stability of old caisson breakwater. In this study, we use the eigenfunction expansion method to analyze the effects of wave structure interaction when new circular caissons are installed on the back or the front of old caissons. The comparison of numerical results between present method and Williams and Li is made, and the wave force and the wave run-up acting on each circular caisson are calculated for various parameters by considering the wave structure interaction.

Investigation of Importance of Evanescent Modes in Predicting the Transformation of Water Waves by the Linear Wave Theory: 2. Numerical Experiments (선형파 이론에 의한 파랑변형 예측시 소멸파 성분의 중요성 검토 2. 수치 실험)

  • 이창훈;조대희;조용식
    • Journal of Korean Society of Coastal and Ocean Engineers
    • /
    • v.15 no.1
    • /
    • pp.51-58
    • /
    • 2003
  • The magnitude of evanescent modes in terms of dynamics it investigated in case that the transformation of water waves is predicted by the linear wave theory. For the waves propagating over two steps, the eigenfunction expansion method is used to predict the amplitudes of reflected and transmitted waves by the component of evanescent modes as well as propagating modes. Then. the relative importance of evanescent modes to the propagating modes is investigated. The numerical experiments find that the evanescent modes are pronounced at the relative water depth of k$_1$h$_1$=0.11$\pi$ and the water depth ratio of h$_2$/h$_1$ close to zero.

Analysis of Multi-directional Random Waves Propagating over Multi Arrayed Impermeable Submerged Breakwater (다열 불투과성 수중방파제를 통과하는 다방향 불규칙파랑의 해석)

  • Jung, Jae-Sang;Kang, Kyu-Young;Cho, Yong-Sik
    • Journal of Korean Society of Coastal and Ocean Engineers
    • /
    • v.19 no.1
    • /
    • pp.29-37
    • /
    • 2007
  • In this study, transmission and reflection of multi-directional random waves propagating over impermeable submerged breakwaters are calculated by using eigenfunction expansion method. A series of mutiderectional random waves is generated by using the Bretschneider-Mitsuyasu frequency and Mitsuyasu type directional spectrum. Strong reflection is occurred at the Bragg reflection condition of the peak frequency. If the row of breakwaters is fixed at 3 and the relative height of breakwater is fixed at 0.6, more than 25% of incident wave energy is reflected to offshore. It is also found that the reflection of directionally spreading random waves increases as the maximum spreading parameter $s_{max}$ increases.

Variation of Reflection Coefficients for a Shelf with Varying Dimensions (선반지형의 크기에 따른 반사율의 변화)

  • Jo, Yong-Sik;Lee, Jong-In;Kim, Yeong-Taek;Lee, Jeong-Gyu
    • Journal of Korea Water Resources Association
    • /
    • v.32 no.6
    • /
    • pp.675-683
    • /
    • 1999
  • The reflection coefficients of monochromatic waves propagating over a shelf with varying dimensions are theoretically calculated. The diffraction of waves by an abrupt depth change is formulated by the eigenfunction expansion method. Not only propagating mode but also evanescent modes are considered in formulation. The role of evanescent modes in reflection coefficients is investigated in detail. Water waves are obliquely as well as normally incident to the region. The obtained reflection coefficients are verified by checking conservation of wave energy.

  • PDF

Characteristics of Heaving Motion of Hollow Circular Cylinder (내부가 빈 원기둥의 수직운동 특성)

  • Bae, Yoon Hyeok;Cho, Il-Hyoung
    • Journal of Ocean Engineering and Technology
    • /
    • v.27 no.5
    • /
    • pp.43-50
    • /
    • 2013
  • In the present investigation, the hydrodynamic characteristics of a vertically floating hollow cylinder in regular waves have been studied. The potential theory for solving the diffraction and radiation problem was employed by assuming that the heave response motion was linear. By using the matched eigenfunction expansion method, the characteristics of the exciting forces, hydrodynamic coefficients, and heave motion responses were investigated with various system parameters such as the radius and draft of a hollow cylinder. In the present analytical model, two resonances are identified: the system resonance of a hollow cylinder and the piston-mode resonance in the confined inner fluid region. The piston resonance mode is especially important in the motion response of a hollow circular cylinder. In many cases, the heave response at the piston resonance mode is large, and its resonant frequency can be predicted using the empirical formula of Fukuda (1977). The present design tool can be applied to analyze the motion response of a spar offshore structure with a moon pool.

Water Wave Interactions with Array of Floating Circular Cylinders (부유식 원형 실린더 배열에 의한 파 상호작용)

  • Park, Min-Su;Jeong, Youn-Ju;You, Young-Jun
    • Journal of Ocean Engineering and Technology
    • /
    • v.27 no.5
    • /
    • pp.51-62
    • /
    • 2013
  • The water wave interactions on any three-dimensional structure of arbitrary geometry can be calculated numerically through the use of source distribution or Green's function techniques. However, such a method can be computationally expensive. In the present study, the water wave interactions in floating circular cylinder arrays were investigated numerically using the eigenfunction expansion method with the three- dimensional potential theory to reduce the computational expense. The wave excitation force, added mass coefficient, radiation damping coefficient, and wave run-up are presented with the water wave interactions in an array of 5 or 9 cylinders. The effects of the number of cylinders and the spacing between them are examined because the water wave interactions in floating circular cylinder arrays are significantly dependent upon these.

Anti-slosh effect of a horizontal porous baffle in a swaying/rolling rectangular tank: Analytical and experimental approaches

  • George, Arun;Cho, Il-Hyoung
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.13 no.1
    • /
    • pp.833-847
    • /
    • 2021
  • The horizontal porous baffle and its effect as an anti-slosh device have been investigated intensively in a swaying and rolling rectangular tank. To accurately assess the level at which porous baffles reduce liquid sloshing, the Matched Eigenfunction Expansion Method (MEEM) has been utilized as an analytical tool. The velocity potentials in the horizontal baffle-covered fluid region are expressed by the sum of the homogeneous and particular solutions to avoid solving the complex dispersion equation. By applying an equivalent linearized quadratic loss model, the nonlinear algebraic equation is derived and solved by implementing the Newton-Raphson iterative scheme. To prove the validity of the present theoretical model, a series of experiments have been conducted with different centered horizontal porous baffles with varying porosities and submerged depths in a swaying and rolling rectangular tank. Reasonably good agreements are obtained regarding the analytical solutions and the experiment's findings. The influence of porosity, submerged depth, and length of a centered horizontal porous baffle on anti-slosh performance have been analyzed, especially at resonance modes. The developed predictive tool can potentially provide guidelines for optimal design of the horizontal porous baffle.

Acoustic Characteristics of Mufflers with an Extended Iinlet and Outlet (입출구가 연장된 동심형 소음기의 음향해석)

  • 이준신;김연환;김태룡;이정권
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 1998.04a
    • /
    • pp.536-541
    • /
    • 1998
  • Cylindrical chamber silencers with an extended inlet and outlet are widely used to reduce the propagated noise in ducts in many application fields. In this study, an acoustic analysis is carried out for concentric extended pipes inserted into a simple expansion chambers An algebraic equation is derived by using the eigenfunction expansion and orthogonality principle. Using this analytical method, transmission losses are predicted for several configurations of the concentric extended systems.

  • PDF