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Working with and evaluating volumes

Forum|Forum|8 years ago
September 2, 2017
30 replies
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Morning to all,

So a few of you have seen I have had varying questions about MC's abilities in the last 24 hours which have lead me to my ultimate question on working with and evaluating volumes.

I am looking to see if MC (and if not taking recomendations for other software) can help me in my next quest.

I am looking at defining a 3D shape (the underwater profile of a ship) and then being able to evaluate the shape i.e. what is its volume, where is its centroid, calculate moments about its centreline etc.

The shape I have in mind can be defined in one of two ways but in both a number of 'slices' of the ship's profile are defined usually in terms of x,y,z ordinates to give a number of 2D profiles either working from front to back or from top to bottom. I know that I could plot each 2D 'slice' in MC and could then evaluate using integration but is it possible to 'put these together' and evaluate the 3D shape in a similar method?

Or is there a better software out there for this? I thought of 3D CAD type softwares but don't know if these have the mathmatical caability of MC (It has been years since I have used CAD software but don't mind getting back into it).

Any thoughts or advice warmly welcomed.

A

PS to give a visual idea of what I am working with below is a google image of the sort of thing where by a number of vertical 'stations' are defined for a ship and I would need to essentially integrate them all to give a volumetric property.

Image result for ship hull station diagram

Statistics_Analysis

Best answer by terryhendicott

How to intergrate along the vessel to get total volume.

Input is the station distances as x ordinates.

Input is the station bouyancy areas as y ordinates.

Integration is total volume.

Trick is to put a smooth spline through the points.

You can then integrate the interpolation of the spline.

Have enclosed MC14, PDF, and data file

Calculation with vessel on the roll requires a different approach but should be possible. DelfShip free gives the metacentric height. The difficulty is the ship on the roll should still have the same bouyancy volume.

T

terryhendicott

21-Topaz II

MathCad is good software. You could create a worksheet that does as you wish. Refer the following which is a mathcad sheet that does just that.

https://ocw.mit.edu/courses/mechanical-engineering/2-082-ship-structural-analysis-design-13-122-spring-2003/calendar/notes_10_shear_bending_fixed.pdf. Poke around this websight and you will get a few more examples.

But it is not necessarily the best for everything. In terms of ship and vessel hulls I recommend the following. It is free!

http://www.delftship.net/DELFTship/index.php/delftship/delftship-free

DELFTship™Free is a fully functional 3D hullform modeling program perfectly suited for students, home users or anyone else with an interest in ship design. And as the name already implies it's completly free of charge!

Model any type of hull. DELFTship™Free is limited to hulls that are symmetrical with respect to the centerplane.
Perform basic hydrostatic and resistance calculations.
View, print and export the traditional 2D linesplan view which is calculated from the 3D model (shaded or black & white).
Use the Lackenby hullform transformation to automatically adjust hull parameters such as displacement and longitudinal center of buoyancy to specified values while maintaining fairness of your model.
Export to various 2D/3D file formats (.STL, .DXF, .OBJ, .GHS etc.)
View plate expansions.

T

terryhendicott

21-Topaz II

This is a Mathcad 14 file. It calculates the bouyancy volume and longitudinal centre of gravity of a real ship at given draft of 3.8m.

I did it to check the results of Delf ship free software. The Mathcad results are the same.

The file reads a DXF file that has been exported from Delf ship. The DXF file are the vertical stations of a vessel hull 31 of them at 2 m apart for the 62 m long vessel. DXF files are single lines of text and can be read and interpreted by MathCad. The calculations are made a bit more complex as some of the station lines start at keel and go to deck, while some start at the deck and go to keel. Splines are used through DXF points to perform intergrations.

The Mathcad reads the DXF file to obtain cordinates of the hull for the calculations. A jpg of the DXF shows the stations and the hull.

Delf is far simpler to use and produces the same results.

1_DELFTship6-1.zip

A

awibroe

Author

1-Visitor

Hi Terry,

I have looked at the MC14 file. Would it theortically be possible to do the same in Prime? I am slightly reluctnat to do all of this in MC 15 as I have not used it to date. I presume you have it in a 14 file as that is what you had when you did the work?

Also, how sophisticated can you get with this? i.e. You have shown that you can calculate underwater volume i.e. buoyancy mass and longitudinal position of centre of buoyancy.

Is it possible to do experiments i.e. see how buoyancy shifts with roll? I am thinking that you could build GZ curves is you are able to observe how the centre of buoyancy moves as the vessel heels?

Thanks,

Andy.

T

terryhendicott

21-Topaz II

Simple station example in Mathcad Prime 4

1_XYZ.zip

A

awibroe

Author

1-Visitor

Hi,

All this looks super impressive and will look at later today in more detail. I don't have Prime 4 but feel like I'm going to need to get the express version to open files people share.

Excellent to know there is some free software for ships specifically out there.

I'll be back soon.

Andy.

T

terryhendicott

21-Topaz II

Hi Andy,

Here is a pdf of the Mathcad 4 sheet that is a calculation at one station of a ships hull. it is an integration vertically

1_StationCalculation.pdf

T

terryhendicott

Answer

21-Topaz II

How to intergrate along the vessel to get total volume.

Input is the station distances as x ordinates.

Input is the station bouyancy areas as y ordinates.

Integration is total volume.

Trick is to put a smooth spline through the points.

You can then integrate the interpolation of the spline.

Have enclosed MC14, PDF, and data file

Calculation with vessel on the roll requires a different approach but should be possible. DelfShip free gives the metacentric height. The difficulty is the ship on the roll should still have the same bouyancy volume.

1_Stations.zip

A

awibroe

Author

1-Visitor

Terry,

So this could in theory be done with my own tabulated data for xyz ordinates?

Definitely going to be looking into DelfShip.

Thanks,

Andy

A

awibroe

Author

1-Visitor

Terry,

That last PDF is really really usefu!

2 follow up questions, is there an intellegent way to integrate each of the stations at once (or is it best to calculate each station area first)? So by this I mean if I have all the data in a matrix for the various point of the hull form (as you have done so by outputting this from a 3rd party softward DelftShip) is there some clever programming I can use to integrate the lot or do I have to work out each station area manually and then input these into a second data set and integrate them all to get the volume as you have done?

What is the CAD issue that would need to be sorted to show vertical centre of buoyancy?

Cheers, really really good stuff!

Andy