Upcoming technical papers and presentations

HydroComp Web Log

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Upcoming technical papers and presentations
Miscellaneous Musings from the Technical Director

Monday, 28-MAY-2007 by Donald MacPherson - Technical Director

Writing technical papers is one of the things that I find really enjoyable about this job. The writing is fun, but it is probably more the discovery of new information that is the best part - in particular, the process of describing a new trend or physical characteristic in numerical terms. For example, past technical papers have presented new prediction formula that we have developed for the effect of cupping or cavitation breakdown.

Our latest effort is a paper with two of my staff - Vin Puleo and Mat Packard - entitled "Estimation of Propeller Properties for Vibration Analysis". Many of you may be familiar with the inertia of entrained water around a propeller (sometimes called "WR²") for torsional analysis calculations. This inertia is one aspect of the added mass of water around a propeller that is being presented in the paper. Here is the abstract for the paper:

The objective of the paper is to provide a summary survey of calculation methods that are available to estimate the material mass and wetted added mass properties of a propeller for vibration analysis. Ranging from simple parametric formula to more robust radius-chord integration, the paper will present and validate calculations for propeller weight, mass moment of inertia, added mass of entrained water (axial), and added mass moment of inertia of entrained water (torsional).

This has proven to be an entertaining journey with a few improved new analyses of old data and a debunking of some traditional estimation formula that are simply awful. The presentation is on June 21st to the New England Section of SNAME.

Once again, I'll be doing a presentation at IBEX in October. I have done a number of IBEX presentations for things like propeller sizing and design, sea trial analysis, and speed prediction. These have all more-or-less been discussions about techniques and procedures relating to the topics. This presentation will be different - a somewhat academic introduction to hydrodynamics for the uninitiated. It is called "Hull Form Hydrodynamics: A Practical Primer".

To meet particular hydrostatic requirements, naval architects typically design hulls from the inside out. For this purpose, a hull's geometry is shaped to conform to the specific volume and centroid required by the internal weight of the boat and its cargo, or by the volume needed for tanks or mechanical spaces. For any given volume and center, however, we can design an unlimited number of different geometries. So, what are the implications of shape from the hydrodynamic perspective? The hydrodynamic requirements of hull form design may be best served by working from the outside in. In other words, sometimes you have to think like the water. Anyone who designs, builds, or operates marine vessels will find this primer on hull form hydrodynamics both interesting and useful. We do not intend to immerse you in a deep academic treatment of the subject, but we do want to equip you with a practical understanding of a variety of fundamental concepts about the relationship between a hull’s shape and how the water reacts to that shape. Along the way, we’ll also dispel a number of common myths.

This one is going to be a lot of fun...