Dynamic Response of Hull Due to Bottom Slamming and Deck Wetness

Hamoudi, Benameur (1995) Dynamic Response of Hull Due to Bottom Slamming and Deck Wetness. PhD thesis, University of Glasgow.

Abstract

When a marine vehicle navigates in rough weather and at high speed, it experiences large motions; these large motions induce heavy responses, such as deck wetness, bottom slamming, rolling, vertical and transverse accelerations. Therefore, in extremely heavy seaways, the ship would generally slow down and/or change the heading angle against the waves to avoid critical conditions arising from such heavy responses. This is confirmed from operation and from experiments where bottom slamming and deck wetness (classified as secondary loads) are found to be severe in head seas at high speed. There is therefore a penalty paid by decreasing the performance and the effectiveness of the marine vehicle. The thesis presents an investigation of two secondary loads applied on a marine vehicle; namely, bottom slamming loads below the waterline structure and deck wetness loads on the above waterline structure, on the deck in particular. At present, these two loads are receiving considerable theoretical and experimental attention (model experiments as well as full scale trial) because of their major influence on local structural design. The first chapter presents an introduction and history of slamming and deck wetness. Bottom slamming and deck wetness events are defined and classified in the range of secondary loads. This chapter also summarizes the considerable work which has been investigated in previous studies carried out on similar subjects by other researchers. The second chapter is concerned with the motion response prediction for a monohull. Full details, of the development of the New Strip Method (NSM), where the end effect of the ship is taken into consideration, is given. The hydrodynamic coefficients are calculated using the Multipole Expansion Method. The excitation forces and moments (Froude Krylov component and diffraction force component) in the right hand side of the equations of motion are presented. The coupled heave and pitch motion equations are solved in the frequency domain. The vertical relative motion is calculated and derived with respect to time to obtain the relative vertical velocity of the wave surface with respect to the mobile ship. This velocity is compared with the threshold value beyond which slamming occurs and prediction of impact pressures due to bottom slamming can be made. In the third chapter, major attention is given to the prediction of pressure due to bottom slamming. Different techniques for the determination of the pressure coefficient such as the conformal mapping technique, deadrise angle prediction technique and experimental prediction technique are detailed and discussed. The use of the two and three parameter pressure coefficient prediction technique is studied and compared with other prediction methods. The occurrence of the bottom slamming phenomenon based on the vertical relative velocity exceeding its threshold value is discussed. Chapter 4 presents an experimental analysis of bottom slamming. A high speed monohull marine vehicle (S175 container ship) was chosen for the experimental investigation of bottom slamming. The ship model was run in regular waves for different forward speeds and wave frequencies which have been carefully chosen to avoid tank wall interference. The instrumentation set-up, calibration of measuring devices and test procedures are presented in this chapter. Theoretical and experimental comparisons of impact pressures due to bottom slamming are presented in chapter 5. Correlation of slamming pressure predictions by theoretical and experimental methods is made to show the validity and the accuracy of the prediction. Spectrum analysis is used to predict the motion behaviour in irregular waves. Moreover, the wave statistical approach is used to predict probability of slamming occurrence, the number of impacts and the extreme loads due to impact pressures which are required for fatigue and ultimate strength design. Other slamming pressure predictions are presented. In chapter 6 theoretical and experimental investigations of the deck wetness phenomenon, on the above waterline structure, namely, the deck structure, are presented. For the first time, a theoretical prediction of the horizontal impact loads, applied to vertical deck-mounted equipment, is formulated and developed. Experimentally, load cells and a catch tank technique are used to quantify load and shipment of water due to the deck wetness event. The statistical wave approach is used to predict the probability of occurrence of deck wetness and the frequency of occurrence in different sea states. Comparison of experimentally obtained data with previous researchers' works is presented. In the last chapter the major findings and conclusions from the research are drawn. Recommendations for future work are made.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: K S Varyani
• Keywords: Naval engineering
• Date of Award: 1995
• Depositing User: Enlighten Team
• Unique ID: glathesis:1995-75732
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Dec 2019 09:15
• Last Modified: 19 Dec 2019 09:15
• URI: https://theses.gla.ac.uk/id/eprint/75732