[논문]Mooring Tension and Motion Characteristics of a Floating Fish Reef with Pipe in Waves and Currents Using Numerical Model

Kim, Tae-Ho

doi:10.5916/jkosme.2010.34.7.997

Mooring Tension and Motion Characteristics of a Floating Fish Reef with Pipe in Waves and Currents Using Numerical Model 원문보기

한국마린엔지니어링학회지 = Journal of the Korean Society of Marine Engineering, v.34 no.7, 2010년, pp.997 - 1008

Kim, Tae-Ho (School of Marine Technology, Chonnam National University)

Abstract ▼ AI-Helper

The mooring line tension and motion response of a floating fish reef system were analyzed using a Morison equation type numerical model. The reef structure was constructed with pipe and suspended up from the bottom with a single, high tension mooring. Input forcing parameters into the model consisted of both regular and random waves, with and without currents. Heave, surge and pitch dynamic calculations were made, along with the tension response in the mooring lines. Results were analyzed in both the time and frequency domains and where appropriate, linear transfer functions were calculated. In addition, damped and natural periods of the system were determined to examine a resonating situation.

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문제 정의

Thus, the system is conservatively designed to withstand environmental loads under waves and currents. In this study, a numerical model study is conducted to investigate the dynamics of a submerged artificial reef system. The reef system is moored by a single, tensioned line.
The objectives of this study are to determine the mooring line tension and motion characteristics of a floating fish reef system with pipe in response to both regular and irregular waves with and without a superimposed current. Numerical models were constructed, simulations were performed and responses were obtained.

가설 설정

The average values in tension, heave, surge and pitch for each of the load cases are provided in Table 5. Using the approach described for regular wave tests, the tension and motion RAO values were calculated and are provided in Table 6. It must be noted the motions(especially heave and pitch) are likely coupled. In addition to the average and RAO values, maximum amplitude values are provided in Table 7.
Typically, the model is built with a predetermined mooring line length, but since the mooring line is actually a spring, upon the initiation of the model run, the buoyancy of the reef component stretches the against the restoring force of the mooring line causing an oscillation. The static heave result shown in Figure 4(b) for the reef system was further investigated with details shown by the solid lines on Figure 8. The damped and natural periods of this oscillation were determined to examine if a resonating situation exists. Assuming an unforced, spring-mass system with linear damping, the system characteristics can be determined by solving the standard, second order, harmonic differential equation(note that the numerical model employs quadratic damping inherent in its formulation).

제안 방법

For each simulation, motion data sets were acquired to characterize the dynamics of the submerged reef structure. Six “nodes” were chosen for which horizontal and vertical movements were analyzed:
0m/sec current. Heave, surge and pitch dynamic calculations were made, along with tension responses in the mooring line. The system has relatively little damping(in heave) with damped natural periods of 6.
The main component of the system is comprised mostly of pipe. In this study, the reef system is analyzed with a numerical model. The numerical model uses the Finite Element Analysis approach described by Tsukrov et al.
The calculations were performed using equations (9) and (10) to obtain the wave elevation(Gηη), heave(Ghh), surge(Gss), pitch(Gpp) and mooring element tension(Gtt) response spectra.
The first set of tests conducted with the reef system was performed with no forcing so that the static characteristics of each system were verified. The next set of tests was performed with the numerical model in regular and irregular waves(JONSWAP spectrum) with and without the 1.0m/sec current. Heave, surge and pitch dynamic calculations were made, along with tension responses in the mooring line.
In addition to the “significant response” results, transfer functions were also calculated. The spectral representation of the wave input, motion response in heave, surge and pitch and the tension responses were calculated. The calculations were performed using equations (9) and (10) to obtain the wave elevation(G_ηη), heave(G_hh), surge(G_ss), pitch(G_pp) and mooring element tension(G_tt) response spectra.

대상 데이터

The model was built using the material and geometric properties provided in Table 2. This model consisted of 158 nodes and 557 elements. The model is shown in detail on Figure 2.

이론/모형

Wave and current loadings on truss and buoy elements were introduced by utilizing the Morison equation[11]. The algorithm employs a nonlinear Lagrangian formulation to account for large displacements of structural elements. In addition, the unconditionally stable Newmark direct integration scheme is adopted to solve the nonlinear equations of motion.
In this study, the reef system is analyzed with a numerical model. The numerical model uses the Finite Element Analysis approach described by Tsukrov et al.[3-4].
The mooring line tension and motion response results of a floating fish reef system with pipe were analyzed using a numerical model results. Using a Morison equation type model, simulations of the system were conducted. The first set of tests conducted with the reef system was performed with no forcing so that the static characteristics of each system were verified.
Numerical model simulations were performed using the finite element computer program developed specifically for marine aquaculture applications. Wave and current loadings on truss and buoy elements were introduced by utilizing the Morison equation[11]. The algorithm employs a nonlinear Lagrangian formulation to account for large displacements of structural elements.

참고문헌 (16)

Korean Ministry of Maritime Affairs and Fisheries, "Installation of artificial reef, pp. 1-5, 2007 (in Korean).
C. G. Kim, H. S. Kim, T. H. Kim and C. I. Baik, "Monitoring of floating fish reef installed in Koje coastal waters", Ocean and Polar, vol. 23, no. 3, pp. 305-310, 2001.

상세보기
I. Tsukrov, O. Eroshkin, D. W. Fredriksson, M. R. Swift and B. Celikkol, "Finite element modeling of net panels using consistent net elements", Ocean Eng., vol. 30, pp. 251-270, 2003.

상세보기
I. Tsukrov, O. Eroshkin, W. Paul and B. Celikkol, "Numerical modeling of nonlinear elastic components of mooring systems", IEEE J. Oceanic Eng., vol. 30, no. 1, pp. 37-46, 2005.

상세보기
J. DeCew, D. W. Fredriksson, L. Bougrov, M. R. Swift, O. Eroshkin and B. Celikkol, " Numerical and physical modeling of a modified gravity type cage and mooring system", IEEE J. of Ocean. Eng., vol. 30, no. 1, pp. 47-58, 2005.

상세보기
D. W. Fredriksson, M. R. Swift, J. D. Irish, I. Tsukrov and B. Celikkol, "Fish cage and mooring system dynamics using physical and numerical models with field measurements", Aqua. Eng., vol. 27, no. 2, pp. 117-270, 2003.

상세보기
D. W. Fredriksson, M. R. Swift, J. D. Irish and B. Celikkol, "The heave response of a central spar fish cage", Transactions of the ASME, J. of Off. Mech. and Arct. Eng., vol. 25, pp. 242-248, 2003.
D. W. Fredriksson, M. J. Palczynski, M. R. Swift and J. D. Irish, "Fluid dynamic drag of a central spar cage open ocean aquaculture IV, June 17-20, St. Andrews, NB, Canada, Mississippi- Alabama Sea Grant Consortium, Ocean Springs, MS. MASGP-01-006, 2001, 2003.
D. W. Fredriksson, M. R. Swift, O. Eroshkin, I. Tsukrov, J. D. Irish and B. Celikkol, "Moored fish cage dynamics in waves and currents", Special issue on open ocean aquaculture engineering. IEEE J. Oceanic. Eng., vol. 30, no. 1, pp. 28-36, 2005.

상세보기
D. W. Fredriksson, I. Tsukrov, K. Baldwin, M. R. Swift and B. Celikkol, "Open ocean fish cage and mooring system modeling", Fisheries Dynamics 2003, National Fisheries Research and Devlopement Institute, Busan S. Korea. pp. 109-122, 2003.
J. R. Morison, J. W. Johnson, M. P. O'Brien and S. A. Schaaf, "The forces exerted by surface waves on piles", Petroleum Transactions, American Inst. of Mining Eng., pp. 149-157, 1950.
N. Haritos and D. T. He, "Modelling the response of cable elements in an ocean environment", Fin. Elem. in Analysis and Des., vol. 19, pp. 19-32, 1992.

상세보기
Y. Goda, "Random seas and the design of maritime structures. World Scientific Publishing Company, New Jersey. 443p, 2000.
www.kordi.re.kr
M. K. Ochi, "Ocean waves: The stochastic approach", Cambridge University Press, New York, 1998.
Shore Protection Manual, 4th ed., 2 Vols., US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, US Government Printing Office, Washing, DC, 1984

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Mooring Tension and Motion Characteristics of a Floating Fish Reef with Pipe in Waves and Currents Using Numerical Model 원문보기

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Mooring Tension and Motion Characteristics of a Floating Fish Reef with Pipe in Waves and Currents Using Numerical Model 원문보기

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