Session: 02-09-01 Extreme Loading and Responses 1

Paper Number: 79056

79056 - Development of Practical Simplified Formula of Wave Pressure in Equivalent Design Wave 

 Since the loads used in the design of a ship (hereinafter referred to as design loads) are, figuratively speaking, located “upstream” in the flowchart typically followed for strength evaluations such as yield strength, buckling strength, and fatigue strength, their accuracy greatly affects the structural dimensions of ship designs. It is for this reason, therefore, quite necessary to estimate such loads as reasonably as possible to ensure accurate strength assessments. Nowadays, it is possible to estimate the design loads reasonably through seakeeping analysis using hull shape information as input data, but such numerical calculations are too difficult and impractical to perform on a per ship design basis; most classification rules, therefore, typically specify a simplified formula for design loads that can be used instead.

 A hull is subjected to not only external wave loads, but also internal loads with different phase differences that are generated by cargo, ballast water, etc. The equivalent design wave method is an approach used to obtain design loads in consideration of the simultaneity of such multiple loads in extreme sea conditions. In this method, the wave height and wavelength of the equivalent design wave are determined by taking into account the sea condition and the characteristics of the response of the hull, and the load acting on the hull can be obtained under these considered conditions.

 Although classification rules often specify design loads based on this method, the application of the Common Structural Rules (CSR) of the International Association of Classification Societies (IACS) is limited to bulk carriers and oil tankers, and this means it is difficult to guarantee the accuracy of these simplified formulae when they are applied to other ship types or ships of other sizes. This study, therefore, proposes a general-purpose and highly accurate simplified formula for hydrodynamic pressure in equivalent design waves. In addition to bulk carriers and oil tankers, 154 models (77 ships x 2 cases in full-load and ballast conditions) of various types and types of ships, including LNG carriers, container ships, and car carriers, were prepared, and numerical calculations were performed using a program based on the three-dimensional Green's function method developed by ClassNK. The numerical calculations were carried out using a program based on the three-dimensional Green's function method developed by ClassNK. By going back to Bernoulli's principle, which is the basic theory of fluid motion essential for considering hydrodynamic pressure, the dominant pressure components of hydrodynamic pressure in equivalent design waves were extracted using these calculation results, and simplified formulas for each of these pressure components were developed. The simplified formulae can be applied to various types and sizes of ships, and their physical meanings are clear and easy to understand.

Presenting Author: Kyohei Shinomoto ClassNK

Authors:

Kyohei Shinomoto ClassNK
Kei Sugimoto ClassNK
Sadaoki Matsui National Maritime Research Institute