• 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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    • 2002.08a
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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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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.

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.

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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    • 2017.11a
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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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Numerical study on supercavitating flow in free stream with regular waves

  • Li, Da;Lyu, Xujian
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.12 no.1
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    • pp.799-809
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    • 2020
  • In this study, the supercavitating flow of a high-velocity moving body near air-water surface is calculated and analyzed based on a commercial CFD software ANSYS Fluent. The effect of regular wave parameters including both wave height and wavelength on the cavitating flow and force characteristics of a body at different velocities is investigated. It is found that the cavity shape, lift coefficient and drag coefficient of the body vary periodically with wave fluctuation, and the variation period is basically consistent with wave period. When the wavelength is much greater than the cavity length, the effect of wave on supercavitation is the alternating effect of axial compression and radial compression. However, when the wavelength varies around the cavity length, the cavity often crosses two adjacent troughs and is compressed periodically by the two wave troughs. With the variation of wavelength, the average area of cavity shows a different trend with the change of wave height.

Experimental studies of impact pressure on a vertical cylinder subjected to depth induced wave breaking

  • Vipin, Chakkurunnipalliyalil;Panneer Selvam, Rajamanickam;Sannasiraj Annamalaisamy, Sannasiraj
    • Ocean Systems Engineering
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    • v.12 no.4
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    • pp.439-459
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    • 2022
  • This paper describes experimental studies of impact pressure generated by breaking regular waves in shallow water on a vertical cylinder. Experimental work was carried out in a shallow water flume using a 1:30 - scale model of a vertical rigid circular hollow cylinder with a diameter 0.2 m. This represents a monopile for shallow water offshore wind turbines, subjected to depth induced breaking regular waves of frequencies of 0.8 Hz. The experimental setup included a 1 in 10 sloping bed followed by horizontal bed with a constant 0.8 m water depth. To determine the breaking characteristics, plunging breaking waves were generated. Free surface elevations were recorded at different locations between the wave paddle to the cylinder. Wave impact pressures on the cylinder at a number of elevations along its height were measured under breaking regular waves. The depth-induced wave breaking characteristics, impact pressures, and wave run-up during impact for various cylinder locations are presented and discussed.

Development of Analytical Solutions on Velocities of Regular Waves Generated by Bottom Wave Makers in a Flume (바닥 조파장치가 설치된 수로에서 규칙파의 유속장에 관한 해석해 개발)

  • Jung, Jae-Sang;Lee, Changhoon
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.34 no.3
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    • pp.58-71
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    • 2022
  • Analytical solutions for two-dimensional velocities of regular waves generated by bottom wave makers in a flume were derived in this study. Triangular and rectangular bottom wave makers were adopted. The velocity potential was derived based on the linear wave theory with the bottom moving boundary condition, kinematic and dynamic free surface boundary conditions. Then, analytical solutions of two-dimensional particle velocities were derived from the velocity potential. The velocity potential and two-dimensional particle velocities which were derived as complex integral equations were numerically calculated. The solutions showed physically valid results as velocities of regular waves generated by bottom wave makers in a flume.

Seakeeping Study of a Container Ship in Regular Waves (콘테이너선의 파랑중 내항성 연구)

  • Yang, Seung-Il;Hong, Seok-Won;Lee, Sang-Mu
    • 한국기계연구소 소보
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    • s.9
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    • pp.193-208
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    • 1982
  • Flap type wave-maker, wave absorber, motion measuring equipment and related instruments were newly installed at Ship Experimental Towing Tank, Ship Research Station, KIMM. The model tests in regular head and following waves were successfully carried out and the motion and wave loads in regular and long crested irregular waves were calculated for a container ship model which was adopted as the hull form for the comparative calculations of the ITTC Seakeeping Committee. The results of model tests show good agreement with calculated results and the latter are generally in good agreement with the results of the comparative calculations.

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