The U.S. Coast Guard operates one of the largest fleets of patrol boats in the world, at a very high operational tempo. Often U.S. Coast Guard patrol boats accumulate over 2500 hours of operation a year in severe sea conditions. In an effort to maximize life expectancy and reduce life cycle cost the U.S. Coast Guard has been involved in a number of efforts to develop operational limitations and hull structural life maintenance strategies for high speed cutters operating in the semi-displacement speed range. Recently model tests have been carried out to validate numerical tools and assess fatigue and ultimate strength, including whipping of semidisplacement patrol boats at a variety of headings. This paper summarizes the results of the model tests that investigated the effects of wave impact and whipping response on the fatigue life and ultimate strength. Findings of measured and computed dynamic loading are compared and revised design considerations are presented. The issue of predicting dynamic response using physical and numerical modeling techniques is addressed, design criteria are critically assessed and finally the importance of structural response monitoring and operator guidance is discussed.

Investigation of Wave Impact and Whipping Response on the Fatigue Life and Ultimate Strength of a Semi-Displacement Patrol Boat

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

The Use of High-Fidelity Numerical Models in Ship Structural Fatigue Predictions

A study on prediction of whipping effect of very large container ship considering multiple sea states

Study of the Prediction of Fatigue Damage Considering the Hydro-elastic Response of a Very Large Ore Carrier (VLOC)

Recently, it has been reported that the whipping response, which is the elastic phenomenon of the ship, may be one of the causes of the ship accident. Unfortunately, the commonly used methodology for evaluating the whipping effect effectively has not been developed yet. In this study, we developed a procedure to estimate the whipping effect of hull in actual design stage. Fluid –structure interaction analysis was performed for a dominant short term sea state to obtain the time series data of vertical wave bending moment including the whipping response by slamming. In order to estimate the whipping effect by using the time series, some signal processing and statistical techniques such as low pass filtering, Weibull fitting and so on, were applied. the hydro-elasticity analysis was performed on container ships of various sizes to evaluate the whipping effect. The parameters that can affect the response of the hull vibration was selected and the effect of these parameters on whipping was analyzed.

A Study on the Whipping Phenomena Effect on the Structural Response of Large Container Ships

It is well known that ships vibrate due to waves. The wave induced vibrations of the hull girder are referred to as springing (resonance) and whipping (transient vibration from impacts). These vibrations contribute to the fatigue damage of fatigue sensitive details. An Ore Carrier of 400 000 dwt is currently being built by DSME, and at time of delivery, it will be the world’s largest bulk (ore) carrier. The scantlings of large ships must be carefully designed with respect to global loading, and when extending the design beyond experience, it is also wise to consider all aspects that may affect operation and the life time costs. The vessel will also enter a long term contract and is therefore to be evaluated for 30 year Brazil-China operation. In order to minimize the risk of fatigue damage, the vessel is designed according to DNV’s class notation CSA-2 requiring direct calculations of the loading and strength. Further it has been requested to include the effect of springing and whipping in the design. Reliable numerical tools for assessing the additional fatigue effect of vibrations are non-existing. DNV has, however, developed an empirical guidance on how the additional effect may be taken into account based on previous development projects related to the effect of vibrations on large ore carriers Due to the size and route of operation of the new design, it has, however, been required by the owner to carry out model tests in both ballast and cargo condition in order to quantify the contribution from vibration. The results from this project have been used for verification and further calibration of DNV’s existing empirical guidance. A test program has been designed for the purpose of evaluating the consequence in head seas for the Brazil to China trade. Full scale measurements from previous development projects of ore carriers and model tests have been utilized to convert the current model tests results into estimated full scale results for the 400 000 dwt vessels. It is further important to carefully consider how the vibrations are to be included in the design verification, and to develop a procedure for taking into account the vibrations which results in reasonable scantlings based on in-service experience with similar designs and trades. This procedure has been developed, and a structural verification has been carried out for the design. The final outcome of the model test was in line with previous experience and in overall agreement with DNV’s empirical guidance, showing a significant contribution from vibrations to the fatigue damage. The springing/whipping vibrations more than doubled the fatigue damage compared to fatigue evaluation of the isolated wave induced loading. The cargo condition vibrated relatively more than experienced on smaller vessels. Various sources to establish the wave conditions for the Brazil to China ore trade were used, and the different sources resulted in significant differences in the predicted fatigue life of the design.Copyright © 2011 by ASME

First Ocean Going Ships With Springing and Whipping Included in the Ship Design

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First Ocean Going Ships With Springing and Whipping Included in the Ship Design