A note of caution about technical papers (example included)

A note of caution about technical papers from the Internet (example included)

This could be a typical case in favor of what I wrote in this post: http://www.boatdesign.net/forums/bo...-high-speed-patrol-boat-43341.html#post559289

Found this recent technical report in Internet: http://pubs.drdc.gc.ca/PDFS/unc35/p522579.pdf
Now, you guys check the Appendix A (pages 64 to 70) and tell me - do you note anything odd?

Without that appendix, it would have been a nice technical report on a very specific CFD research.
But with that appendix, a question arises: was that research work checked/verified by a person experienced in ship design or in hydrodynamics?

The Appendix A clearly wasn't properly peer-reviewed, so I can guess that neither was the rest of the report. Still, it is now a part of an official document published in Internet by an authoritative source (Canadian Defence R&D).

Morale of the story:
If you are searching for info in Internet, keep your eyes wide open, read every line critically and compare it with other research and with your proven knowledge. The more (info) is better in that case.
If you are preparing technical reports to be publicly distributed, stick to the assigned task and don't overdo. Less is better in that case.

Cheers

P.S.
Please let me repeat the question, because it is a fulcrum of this story: Can you guys tell what's wrong with the case shown in the Appendix A (pages 64 to 70)?

 

Rn=29.400.000 not 23.500.000 ?
also the hull is immersed in a weird manner...

 

The Reynolds number and scaling? I was also wondering about the free surface.

 

Yes, the absence of free-surface effects is an immediately noticeable problem. The flow speed in the CFD simulation is around 6.8 kts, a fast displacement speed regime. At that speed waves cannot be ignored and would significantly deform the free surface around the hull. Yet, the model looks like it is running at just 1 kts or somewhere around that. It also invalidates all their conclusions about the pressure distribution around the hull and about the flow behind the transom, whole 4 pages of colored pics and explanatory text ripe for a trash bin...

About the Reynolds number - we cannot tell it's exact value, as we don't know whether 6 meters is the LOA or the LWL. But we do know it is somewhere around 20 million. Pretty high Re and hence fully turbulent flow, so it is not a significant issue here.

Scaling - that is also an unknown (and hence perhaps not a major issue here), because we don't know if this is a CFD simulation of a full-size boat or of a scale model.

 

It looks like they submerged the entire hull, not only up to the DWL. And there doesn't seem to be any regard for free surface effects, they just treated it analogous to the submarine case. To see something like this published is quite embarrassing.

I remenber when I was pursuing a masters degree I read a series of papers from an institue in England that were all exact copies of one another. Copies of paragraphs and smaller bits was quite common overall. After that experience I treat "scientific papers" with a lot of doubt. It's turned in to a big "publishing industry", since academics are mostly evaluated by how much papers the publish, not their actual quality.

 

I agree, it has become a real problem. When science becomes exclusively a branch of marketing and business, and no more a motor for intellectual progress of the humanity, then we indeed do have a problem regarding the truthfulness of the data (apart the relative moral issues).

 

So, If there are this kind of mistakes at the illuminated surface of pictures, what could remain under the dark depth of numbers...
Daikiri, give us another one!

 

I tend to look at the publication as much as the article. IE if something appears in a reputable publication then it holds more weight with me than something from some industry rag.

not being a naval engineer this issue is of particular importance to me.

conflicting advice is something that I find particularly irksome

 

Perhaps the title of this thread should have been "A note of caution about technical papers" because the criticism would be equally valid for a paper copy of the report found on a library shelf, perhaps a shelf in a university or corporate library which receives copies of government publications.

To keep the report given as an example in context the report is titled "Estimating Drag Forces on Submarine Hulls" and there doesn't appear to be any mention of free surface effects anywhere. The hulls and shapes evaluated are all treated as submerged well away from the free surface or any other surface. It would have been more accurate if the author of the report, a senior (4th year) undergraduate in a Canadian university, had said Appendix A showed the application of the methodology to a somewhat arbitrary shape which happens to coincide with the shape of a yacht hull. As written it's a overstatement of the applicability of the method, something I've seen in peer reviewed papers and articles.

I've also seen technical reports by technical reports by senior staff of respected and in some case esteemed research facilities which had more fundamental and significant flaws. One case I remember from thirty five years ago, when reports were typed and figures hand drawn, was over 300 pages in length and had a model of a phenomena which was claimed to be based on fundamental physics developed over years of previous work. Of course a few coefficients needed to be determined based on the experimental data. The final formula for predicting the phenomena filled a page. However with considerable mathematical manipulation the formula could be reduced to a simple four term truncated Fourier series with four coefficents which were specifically derived for each set of data. In other words a simple curve fit exercise hidden in 300 pages, the result of several years of research. And nothing to do with the internet.

 

Your words sound correct to me, David. Whish I could correct the title, but I don't see that option available anymore. Time has ran out, I'm affraid.
The reference was given to papers distributed freely through the Internet because it has (imo) become one of the main sources of info for non-professional designers and builders as well as for students from all around the world - as we can witness at this forum too.

 

One of the reasons there may not have been a reference to surface effects, is the focus seemed to be for submarines. Though I just skimmed the paper, and didn't read it closely.

 

Also one has to remember that the internet is open to people with agendas publishing whole series of fallacies as truth in order to promote their agenda.

 

The Appendix A, the way it is written, just shouldn't be there. It has nothing to do with submarines and is physically completely incorrect if it was intended as a case study of a surface vessel. I find it really incredible that the reviewer of the paper (if there was any) didn't notice how inconsistent and disconnected from the reality is the example of that boat.

 

Select the subject you know best, then read the Wikipedia entry, and you are likely to find problems with the information. Often times, serious problems. That's the level of accuracy you should expect when reading entries on subjects you know nothing about. Not encouraging. Everything needs to be resourced and checked before you give it too much credence.

 

I just wouldn't rely all that much on Undergrad senior capstone projects, although doing CFX on a submarine is pretty impressive for such a project.