Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

In this study, a measurement method concerning dynamic shaft bearing loads resulting from axial vibrations in a propulsion shaft system of a megayacht was developed. Axial shaft vibration measurement set-up was designed, materials of the experiment were selected and the steps of the measurement were defined. 

The main aim of the thesis is to determine the forces coming from the propeller. A new method was developed to calculate these forces. This method is based on modal analysis and mobility function which is the back bone of the modal analysis. Therefore an experimental set-up and the steps of the experiment were developed uniquely in order to obtain the mobility function of the shaft line for megayachts in motion. 

An example experiment was designed for a particular motor yacht. All the materials and the tools were selected according to particulars of this megayacht. However the steps of the experiment can be applied to any yacht and are given in a table in conclusion. 

The main challenges of the thesis are applying the excitation force and finding suitable tools for the experiment. The measurement of vibration is desired to be performed on a yacht as built. Laboratory devices and conditions are not valid any longer. The spaces around the shaft, real working conditions of the yacht and the lack of convenient excitation methods are all obstacles for this experiment. There are many different types of excitation methods like pressurized air, acoustics, electromagnetic excitation and laser. They are all non-contact type excitation methods but they have different drawbacks and are not suitable to be used in this measurement. 

On the other hand an impact hammer which is a contact type excitation method and also dangerous to be used on rotating shaft can be a solution. It has also disadvantages and is not a perfect solution, but it was decided to be used with special modifications and additional devices. It is a special impact hammer which can be controlled automatically. 

Hitting in axial direction to the 34 ton of propeller and the shaft which is rotating with 188 rpm is the particular case considered here. Moreover there is just one suitable place to hit the shaft. It is a flange which is full of bolts. Therefore two different solutions were developed to enable to hit the flange: covering the bolted face of the flange by additional steel plate and attaching the impact hammer to the shaft. The first one needs extra design of plates. In the second option, an automated impact hammer is attached to the shaft and can be remote controlled. These designs reduce many drawbacks of the impact hammer. 

The thesis was developed as theoretical basis because of the lack of an on-going megayacht project in the shipyard during the thesis. Therefore performing the measurement and confirming of the method can be a future study.

Ingénierie, informatique & technologie > Ingénierie civile

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Increasing economic and industrial activities in Polar Regions require new engineering solutions to deal with arctic hazards. One of the main challenges for vessel navigation in ice are pressure ice ridges — sets of randomly oriented large pieces of sea ice along a line with keel and sail parts. These ice ridges may affect the normal exploitation of ice-going vessels, subsea pipelines, and equipment.
The objective of this master thesis was to develop and implement algorithms in a numerical tool, capable of simulating the process of ship hull breaking through pressure ice ridge. The tool is based on the idea to implement Discrete Element Method (DEM) and corresponding code developed at Hamburg Ship Model Basin (HSVA) for simulation of ice ridges creation.
In the thesis the following aspects have been covered: theoretical information on pressure ice ridges and the processes of their creation in nature and ice tank; review of available at present methods to estimate ridge and structure interaction; general idea of DEM and its application; ridge and hull interaction.
In the present project the author focuses on the following: modification of theoretical DEM algorithms in order to be adopted for ridge breaking simulation; method to introduce and to treat complex concave hull geometry with existing DEM software, taking into account adopted data structures of three-dimensional DEM; calculation of hydrostatic properties, inertial and other relevant characteristics of the ship hull (buoyancy, thrust, gravity, restoring forces); numerical integration of equations of motion of ship as discrete element in order to observe realistic performance of the vessel in an ice ridge. Interaction with level ice is not simulated but implemented in the form of an added ice resistance based on semi-empirical formulae of Lindqvist (1989).
The software is able to provide visualization of ship hull/ice ridge interaction, calculate ship resistance, position, velocity, acceleration, thrust, and other relevant parameters during breaking through an ice ridge, and simulate ramming operations corresponding to reality when ship is getting stuck in the ridge.
The code has been validated with corresponding experimental data, provided by Hamburg Ship Model Basin. The results have been discussed and proposals for further calibration and validation of the existing model have been given. Finally some ideas are expressed on how to use developed methods to simulate interaction of floating structures with other types of ice formations.

Ingénierie, informatique & technologie > Ingénierie civile

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Underwater Explosions (UNDEX) have been a subject of high interest not only for military organizations but also for commercial industry. The analytical and numerical tools that have been developed until these days have allowed studying the energy transport mechanisms occurred in UNDEX and its interaction with man-crafted structures, allowing also improving the structural scantlings and defense systems against these kinds of treats. Similar approaches can be used as well to study the instantaneous high-pressure impact loads such as slamming, which is one of the most important design loads in the vast majority of applications in naval engineering. However, performing experimental tests of these mechanisms is not only a costly but also a complicated process, due to the hazards involved in handling explosives and the limited organizations that have licenses to develop such tests.
Under the framework of Project SUCCESS, one of the main objectives is to study the response of Fiber Reinforced Polymers (FRP) structures subjected to slamming and UNDEX, therefore developing accurate calculation tools, which allow the designers to take into account these loads in the design of different naval components. One of the main challenges of the project is to include adequately the intra-laminar and inter-laminar damage mechanisms during these events, which is far more complex to the ones suffered by metallic materials. For these reasons, a series of experimental tests were performed in order to understand the dynamic behavior of FRP square plates subjected to soft body projectile impacts, while validating the numerical models developed.
The research performed in this Master thesis was focused in the use of Arbitrary Lagrangian Eulerian (ALE) methods for solving Fluid Structure Interaction (FSI) problems involving Soft Body Impacts on composite laminates, focusing mainly in the structural behavior of the plates during the impact, especially the intra-laminar damage mechanisms and its evolution. Simplified models of composite damage are used to predict the different phases of the plate response: elastic response, initiation of matrix cracking due to tension loads and finally fiber rupture. The initial results of the numerical models were used as a reference for the gas canon tests performed during the project campaign.

Ingénierie, informatique & technologie > Ingénierie civile