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Research Papers: Offshore Technology

Model Tests of a Caisson in Wet Towing for Assessing Resistance and Stability in Calm Water and Waves

[+] Author and Article Information
Chang-Wook Park

School of Earth and Environmental Sciences,
Seoul National University,
Seoul 08826, South Korea

Jeonghwa Seo

Research Institute of Marine
Systems Engineering,
Seoul National University,
Seoul 08826, South Korea
e-mail: thamjang@snu.ac.kr

Shin Hyung Rhee

Research Institute of Marine
Systems Engineering;
Department of Naval Architecture
and Ocean Engineering,
Seoul National University,
Seoul 08826, South Korea

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received October 13, 2017; final manuscript received February 22, 2018; published online April 26, 2018. Assoc. Editor: Celso P. Pesce.

J. Offshore Mech. Arct. Eng 140(5), 051301 (Apr 26, 2018) (9 pages) Paper No: OMAE-17-1188; doi: 10.1115/1.4039866 History: Received October 13, 2017; Revised February 22, 2018

A series of model tests of a caisson in wet towing were conducted in a towing tank to assess the stability and effective power requirement in calm water and head sea conditions. The scale ratio of the model was 1/30, and the model-length-based Froude number in the tests ranged from 0.061 to 0.122, which is equivalent to 2 and 4 knots in the full scale, respectively. During the towing of the model, tension on the towline and six-degrees-of-freedom (6DOF) motion of the model were measured. Under the calm water condition, the effects of towing speed, draft, and initial trim variation on the towing stability and effective power were investigated. Initial trim improved stability and reduced required towing power. In head seas, effective power and towing stability were changed with the wavelength. It increased as the wavelength became longer, but the added resistance in long waves also stabilized the model with reduced yaw motion.

Copyright © 2018 by ASME
Topics: Stability , Caissons , Waves , Tension , Water , Seas , Yaw
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Figures

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Fig. 1

Design of the caisson and slit covers

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Fig. 2

Design of the scaled model (left) and manufactured acrylic model (right)

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Fig. 3

Variation in the GM and displacement with draft change

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Fig. 4

Arrangement of the test model and towline in the model test

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Fig. 5

Time history of results of the free roll decay and free pitch decay tests

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Fig. 6

Time history of tension and 6DOF motion measurement results in the main case

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Fig. 7

FFT analysis results of pitch angle and surge acceleration of the model and tension on the towline in the main case

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Fig. 8

FFT analysis results of roll angle and sway acceleration of the model in the main case

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Fig. 9

FFT analysis results of yaw angle of the model in the main case

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Fig. 10

FFT analysis results of tension on the towline with α variation

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Fig. 11

FFT analysis results of tension on the towline in waves at H/λ of 1/50

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Fig. 12

FFT analysis results of pitch motion and surge and heave acceleration of the model in waves at H/λ of 1/50

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Fig. 13

FFT analysis results of roll and yaw motion and sway acceleration of the model in waves at H/λ of 1/50

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Fig. 14

Prediction of PE for wet towing of the caisson in head seas

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Fig. 15

Standard deviation of the yaw motion of the caisson model in head seas

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