טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMazaltrim Elad
SubjectDesign of Fast Boat Hull Made of Composite Materials
Considering Hydro-Elasticity
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Nitai Drimer
Full Thesis textFull thesis text - English Version


Abstract

Typically, the dominant load being applied to the hull of a planning boat and dictates its structure is the slamming pressure when the boat sails fast at head seas, where the bow (or even the whole boat) rises from the water surface and then slams it.

According to design rules for high speed vessels, the required strength calculations apply beam theory under quasi static pressure, to determine the different load - bearing elements (plate, stiffeners, etc.) of the hull, which are simplified to beams.

During the last 20 years, as computer hardware evolved and methods for fluid - structure interaction (FSI) modelling were introduced, numerical simulations gradually became the major means in the slamming field of research.

This study is a continuation to studies carried out in the research group:

1.         A method of designing a body of surf boats, considering hydro-elasticity by Moskowitz ?[13].

2.         Design a fast boat body for Limit state situations by Neuberg ?[14].

These studies presented that by considering the physics of hydro-elasticity in the slamming of fast boat made of aluminum, a designer could significantly reduce boat's weight (about 20%) or alternatively increase the boat’s sailing speed in a specified sea state.  The researchers concluded that stress development in the material during the actual dynamic interaction is smaller than that assessed by the quasi static loading procedure.  In addition, the lighter vessel could still comply with the allowable stresses specified by the classification societies.  In these studies, the boat’s hull was analyzed as thin strips with appropriate boundary conditions (2D model), which is a common approach in naval architecture.

In this study we implement the novel rational design procedure described above, to the design of fast boats made of composite materials.

From investigation of several composite materials and from the conclusions of previously published researches of aluminum vessels, it is concluded that the implementation of the novel rational design has greater importance in aluminum hulls compared to a design with typical composites. The advantage toward aluminum is related to the difference between the linear failure criterion and the actual stress development while considering the physics in the rational design.  Not as in aluminum, this difference is smaller for typical composites due to the brittle behavior of the matrix.

To better benefit the hydro-elastic effects, and the potential of saving material by a rational design, we found that the designer should consider “Thermoplastic” composites.  In this type of composites, considering hydro-elasticity is effective in certain range compared to a design by rules and allows to increase the operational envelope of speed versus sea-state by about 10%.