• Title, Summary, Keyword: Regular wave

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Application of a Regular Wave Model to Calculation of Irregular Wave Reflection from Perforated-Wall Caisson Breakwaters (불규칙파의 유공 케이슨 방파제로부터의 반사율 산정시 규칙파 모델 적용)

  • Suh Kyung Duck;Son Sang Young
    • Proceedings of the KSME Conference
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    • pp.205-208
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    • 2002
  • Numerous studies have been performed to develop an analytical model that can predict the reflection of regular or irregular waves from a perforated-wall caisson breakwater. Though such irregular wave models as Suh et at. (2001) become available, regular wave models are still in extensive use because of their simplicity. In the present study, using the regular wave model of Fuggazza and Natale(1992), the reflection of irregular waves from a perforated-wall caisson breakwater was calculated in several different methods. First, the regular wave model was re-validated by the hydraulic model tests. Though the model somewhat over-predicted the reflection coefficients at larger values and under-predicted them at smaller values, overall agreement was pretty good between calculation and measurement. Then, the regular wave model was applied to calculate the irregular wave reflection in the experiments of Suh et at.(2001) and Bennett et al. (1992). In applying the regular wave model to irregular wave reflection, several different methods were used. The results showed that it is the most reasonable to use the regular wave model repeatedly for each frequency component of the irregular wave specuum with the root-mean-squared wave height for all the frequencies .

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Experimental Study on Nonlinearity Characteristics Near the Free Surface in the Regular Wave Condition

  • Choi, Hae-Jin;Jung, Kwang-Hyo;Suh, Sung-Bu;Jo, Hyo-Jae;Choi, Han-Suk
    • Journal of Ocean Engineering and Technology
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    • v.24 no.1
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    • pp.1-9
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    • 2010
  • A series of experiments employing particle image velocimetry (PIV) technique was conducted to produce benchmark wave kinematics data for regular waves having four different wave slopes in 2-D wave tank. Water velocities and accelerations near the free surface of regular waves were computed from image pair obtained by PIV systems. With the measured wave velocity field, the wave accelerations were computed using a centered finite difference scheme. Both local and convective components of the total accelerations are obtained from experimental data. With increasing the wave slope, the horizontal velocity and the vertical accelerations near the wave crest obtained by PIV technique became larger than theoretical results, which are well-known phenomena of the wave nonlinearity. It is noted that the relative magnitude of convective acceleration to the local acceleration became larger with increasing wave slope.

On the Calculation of Irregular Wave Reflection from Perforated-Wall Caisson Breakwaters Using a Regular Wave Model (규칙파 모델을 이용한 유공케이슨 방파제로부터의 불규칙파 반사율 산정에 대하여)

  • 서경덕;손상영
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.15 no.1
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    • pp.11-20
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    • 2003
  • In this paper we examine several methods tor calculating the reflection of irregular waves from a perforated-wall caisson breakwater using a regular wave model. The first method is to approximate the irregular waves as a regular wave whose height and period are the same as the root-mean-squared wave height and significant wave period, respectively, of the irregular waves. The second is to use the regular wave model, repeatedly, for each frequency component of the irregular wave spectrum. The wave period is determined according to the frequency of the component wave, and the root-mean-squared wave height is used for all the frequencies. The third method is the same as the second one except that the wave height corresponding to the energy of each component wave is used. Comparison with experimental data from previous authors shows the second method is the most adequate, giving reasonable agreement in both frequency-averaged reflection coefficients and reflected wave spectra.

Comparative Study on Wave Induced Fatigue Analysis Methods for Steel Catenary Riser (파랑하중에 의한 Steel Catenary Riser 피로손상 평가 방법의 비교검토)

  • Lee, Jeong-Dae;Lee, Sung-Je;Jang, Chang-Hwan;Jun, Seock-Hee;Oh, Yeong-Tae
    • Journal of the Society of Naval Architects of Korea
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    • v.52 no.3
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    • pp.222-235
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    • 2015
  • The purpose of this study is to suggest guidelines for riser fatigue analysis in terms of selection of reasonable analysis method. Three analysis methods (spectral, regular wave, rain-flow counting) are introduced and compared. As the riser systems give non-linear response, the time-domain analysis method is more preferred than frequency-domain analysis method. The spectral fatigue analysis method, however, is still useful for identifying fatigue prone areas. Once stress RAO is established, fatigue damage can be calculated very quickly. The regular wave method and the rain-flow counting method are more time consuming but give more exact results compare to spectral method. In case of regular wave method, a set of regular waves which represent random sea states is considered for dynamic analysis. The rain-flow counting method is the most intuitive and exact method because it refers time history stresses containing most of non-linear effects of the riser system. However, it is not common for early design stage to use rain-flow counting method because of its high cost. In this study, it was confirmed that the regular wave method is the most cost effective way in specific cases. However, if the system is highly non-linear, it seems that the regular wave method gives less accurate results than rain-flow counting method. Therefore, it is imperative that the engineers select appropriate analysis method based on design stage and given engineering period. This paper also discusses the theoretical background of each calculation method and hydrodynamic aspects of marine riser systems. A steel catenary riser (SCR) line on FPSO was considered and marine dynamic program (OrcaFlex) was used for static and dynamic analysis.

Experiments for Wave Transformation of Regular and Irregular Waves over a Submerged Elliptic Shoal(I) : Non-breaking Conditions (타원형 수중천퇴상의 규칙파 및 불규칙파의 전파변형 실험(I):비쇄파조건)

  • 이종인;이정욱
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.14 no.3
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    • pp.240-246
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    • 2002
  • Hydraulic model experiments were conducted fur a series of regular and uni-directional irregular waves propagating over a submerged elliptic shoal. Two different sets of experiments have been studied; one considers regular wave transformation with no breaking, and the other considers uni-directional irregular wave with partial breaking on top of the shoal. The numerical experiments are also performed using a numerical model based on the parabolic approximation equation. The result of the numerical experiments are compared with that of hydraulic experiments.

Experimental Study on Force and Yaw Moment Acting on Ship in Regular Wave with Various Wave Direction

  • Nguyen, Van-Minh;Yoon, Hyeon-Kyu
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • pp.19-21
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    • 2017
  • Ship maneuvering performance is usually estimated in calm water conditions which provide valuable information about the ship maneuvering characteristics at the early design stage. However, the course-keeping ability and the maneuvering performance of a ship can be significantly affected by the presence of waves when ship maneuvers in real sea condition. Therefore, it is necessary to understand the maneuvering behavior of a ship in waves in the viewpoint of ship safety in the design stage. In this study, the force and yaw moment acting on a moving ship in regular waves with different wave length and wave direction will be performed in the square wave tank in Changwon National University. The results of this study can be used to help a person to design a ship hull with the best ship maneuverability in waves and disseminate knowledge on predicting ship maneuvering in regular waves in various wave directions.

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Experimental Study on Flow Characteristics of Regular Wave Interacting with Rectangular Floating Structure Using PIV Technique (PIV시스템을 이용한 규칙파중 2차원 사각형 부유식 구조물 주위의 유동특성 연구)

  • Jung, Kwang-Hyo;Chun, Ho-Hwan
    • Journal of Ocean Engineering and Technology
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    • v.20 no.6
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    • pp.41-53
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    • 2006
  • This experimental study investigated the flow characteristics for regular waves passing a rectangular floating structure in a two-dimensional wave tank. The particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The phase average was used to extract the mean flow and turbulence property from repeated instantaneous PIV velocity profiles. The mean velocity field represented the vortex generation and evolution on both sides of the structure. The turbulence properties, including the turbulence length scale and the turbulent kinetic energy budget were investigated to characterize the flow interaction between the regular wave and the structure. The results shaw the vortex generated near the structure corners, which are known as the eddy-making damping or viscous damping. However, the vortex induced by the wave is longer than the roll natural period of the structure, which presents the phenomena opposing the roll damping effect; that is, the vortex may increase the roll motion under the wave condition longer than the roll natural period.

Behavior of Regular Waves and Multi-Directional Random Waves Passing a Breakwater (방파제를 통과하는 규칙파와 다방향 불규칙파랑의 거동)

  • Park, Sang-Il;Park, Jin-Ho;Cho, Yong-Sik
    • 한국방재학회:학술대회논문집
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    • pp.439-442
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    • 2008
  • Diffraction of multi-directional random waves passing semi-infinite breakwater is investigated by using analytic solution derived by Penny and Prices(1952). An irregylarity of period and incident angle of waves and regular periods for regular waves are considered in addition by expanding from the past study which used only monochromatic wave in general. The Bretschneider-Mitsuyasu frequency spectrum and Mitsuyasu directional spectrum are used for incident waves. And diffraction of multi-directional random waves is reappeared by decomposing numerical results of several monochromatic waves which have variable period and incident angle. Analytic solution on the diffraction of regular waves and multi-directional random waves calculated in this study.

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Research on Wave Kinematics and Wave Loads in Breaking Wave (쇄파의 유동구조 및 쇄파력에 관한 연구)

  • Lee, Soo-Lyong;Kang, Byung-Yoon;Lee, Byeong-Seong
    • Journal of Ocean Engineering and Technology
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    • v.21 no.1
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    • pp.18-24
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    • 2007
  • When the wind blows strong, most waves are breaking at sea. Breaking waves occur by exceeding the limitation of wave steepness (wave height/wave length = 1/7). Because a wave of single angular frequency couldn't generate the breaking phenomena at a two-dimensional ocean engineering basin, the breaking wave can be generated by the superposition of waves with various angular frequencies based on dispersion relation. This study investigates the particle kinematics in the breaking wave and the magnitude of the breaking wave exciting force at the breaking point and breaking region. We compare the regular wave load in a regular wave, which has same specifications (wave height, period and length), with the breaking waveload. Also, the experimental results of wave exciting force and particle velocity are investigated, by comparison with the analytic results using the potential theory.

Adaptive Re-reflecting Wave Control In Plunger Type Wave Maker System: Experiments In Two Dimensional Wave Basin

  • Park, Gun-Il;Kim, Ki-Jung;Park, Jae-Woong;Lee, Jin-Ho
    • Journal of Ship and Ocean Technology
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    • v.7 no.1
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    • pp.13-18
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    • 2003
  • The control performances for active re-reflecting wave control suggested in the previous paper have been verified in cases of regular and irregular waves in a real two dimensional wave basin. For regular waves, the control performances are investigated in terms of reflection coefficients, expected amplitudes of propagating waves and wave absorbing capabilities after cessation of wave generation, compared with those of no-control cases. For irregular waves similar verification procedures were adopted. Though there are certain constraints due to the geometrical non-linearity of wave maker and certain nonlinear characteristics due to the near field and gravity waves these experiments show that the control logic could be useful in realizing re-reflecting wave control in conditions of real wave basin.