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Structures and Safety Reliability

Critical Situations of Vessel Operations in Short Crested Seas—Forecast and Decision Support System

[+] Author and Article Information
Günther F. Clauss, Daniel Testa

Ocean Engineering Department,  Technical University Berlin, Salzufer 17-19, SG 17, 10587 Berlin, Germany

Sascha Kosleck1

Ocean Engineering Department,  Technical University Berlin, Salzufer 17-19, SG 17, 10587 Berlin, Germanykosleck@naoe.tu-berlin.de

1

Corresponding author.

J. Offshore Mech. Arct. Eng 134(3), 031601 (Feb 02, 2012) (15 pages) doi:10.1115/1.4004515 History: Received July 27, 2009; Revised March 30, 2011; Published February 02, 2012; Online February 02, 2012

The encounter of extreme waves, extreme wave groups, or unfavorable wave sequences poses dangerous threats for ships and floating/stationary marine structures. The impact of extreme waves causes enormous forces, whereas an unfavorable wave sequence—not necessarily extreme waves—can arouse critical motions or even resonance, often leading to loss of cargo, ship, or crew. Thus, besides a well thought-out maritime design, a system detecting critical incoming wave sequences in advance can help avoiding those dangerous situations, increasing the safety of sea transport or offshore operations. During the last two years a new system for decision support onboard a ship or floating/fixed marine structure named CASH—Computer Aided Ship Handling—has been introduced. The preceding papers showed the step wise development of the main components of the program code—3d-wave forecast and 3d-ship motion forecast . These procedures provide a deterministic approach to predict the short crested seas state within radar range of the ship, as well as resulting ship motions in six degrees of freedom. Both methods have been enhanced with special focus on the speed of calculation to ensure a just-in-time forecast. A newly developed component is the adaptive 3d-pressure distribution . This method calculates the pressure distribution along the wetted surface of the ship hull using a newly developed stretching approach. With the end of the joint project Loads on Ships in Seaway (LaSSe), (funded by the German Government) the paper presents the CASH system, giving the possibility to detect critical situations in advance. Thus not only decision support onboard a cruising ship can be provided, but also time windows for offshore operations are identified well in advance.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Workflow of the CASH-system for Computer Aided Ship Handling

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Figure 2

wave forecast method: uni-directional, long crested seas (left), multidirectional, short crested seas (right)

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Figure 3

Global coordinate system with sector-wise segmentation of encountering wave components (top left side), sector-wise segmentation of encountering wave components in ship-fixed coordinate system (bottom left side), sector-wise encountering wave trains and their superposition (right side)

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Figure 4

Contribution to overall pitch motion due to the encountering wave train in one of the sectors

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Figure 5

Transformation of table form spectrum to matrix form spectrum—splitting into four sub-matrices, point symmetric to their origins (kx , ky  = 0), with complex and conjugate complex components

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Figure 6

Flow chart 2D-IFFT procedure of the 3d-wave forecast method

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Figure 7

Change of Response Amplitude Operators as well as sea state and response spectra according to the cruising speed of the ship (for waves encountering from 195°)

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Figure 8

Change of the overall time-domain ship responses, as a superposition of the sector-wise derived responses, for heave, roll, and pitch motions in dependency on the implementation of the roll damping coefficient

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Figure 9

Predicted surface elevation maps (snapshots) of the sea state in radar range of the ship from 0 to 180 s

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Figure 10

Predicted ship responses for heave, roll, and pitch motion as well as the corresponding acceleration at a cruising speed of 14 kn

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Figure 11

Predicted ship responses for heave, roll, and pitch motion at three different cruising speeds [11 kn (top), 14 kn (middle), 17 kn (bottom)]

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Figure 12

Predicted wave field in the proximity of the ship at t = 72.13 s [without ship (top), with ship (bottom)]

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Figure 13

Predicted distribution of the dynamic pressure in the proximity of the ship at t = 72.13 s [without ship (top), with ship (bottom)]

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Figure 14

Predicted distribution of the dynamic pressure on the ship hull at t = 72.13 s (top: port, bottom: starboard; dark gray: high pressure, light gray: low pressure)

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Figure 15

Predicted distribution of the absolute pressure on the ship hull at t = 72.13 s (top: port, bottom: starboard; dark gray: high pressure, light gray: low pressure)

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