Can't get volume of oil tank - 1 component in 5 parts

volume

#1

[Sketchup Make 2016] I have created a model of my oil tank - a ribbed cylinder with 4 supports, all of which fill with oil. The cylinder part has a volume of 1745 litres (shown as 1745,xxx,xxx cubic millimetres). When I select the whole model and triple click on it, the entity info shows this volume figure, but I know this excludes the 4 supports which are not in blue.
The entity info confirms the model is a single component.
I have used ThomThom’s CleanUp3 but this has not solved the problem.
Trying to delete extra lines and faces only opens up the structure, and all of the faces seem to be the same orientation.
What’s the trick to joining it all up?
Oil tank 4.skp (266.2 KB)


#2

There are several problems. Your model is built of nested components. This prevents their geometry from interacting, and that evidently confuses SU’s calculation of the total volume. They also create closed interior volumes that don’t have any openings between them, which again is probably confounding SU’s volume calculation:


#3

If all else fails you can use the fact much of geo modeled in SU winds up as a Prismatoid and the vol of those is just the surface area (2D) and extruded length x that area. You will have to count some of the internals negative vol.
Luckily you have made all the items components so there is no reason you cant get the vol each component. Note one of the supports looks differnt than others, on purpose(?) and part of those will have to counted as neg vol.
I get the total tank ~1.743 cubic meters, ThaTs w/o support consideration.


#4

Thanks very much @slbaumgartner. I suspected that it was made of more than one component. Obviously the whole thing is a component, but how can I identify other components, and is there a way of stopping a set of parts being a component?
Your demonstration of the section moving across is very helpful. I have managed to remove some of the internal faces, but removing others causes unexpected openings.


#5

Thanks @mac7595. All the supports are supposed to be the same!

Not done on purpose. Actually, I made the cylinder part in SU 2016 and used ThomThom’s CleanUp3 to get that correct (i.e. to show the volume). Then SU 2017 came out and I added the supports using that version, but needed to convert back to 2016 to use CleanUp3 again, so exported as a 3ds file and re-imported to 2016, which created the format.

The actual volume I created is probably wrong. I just want a working model to produce a graph of the change in volume as the oil height decreases, then I will apply a factor to correct to the known actual volume of 1380 litres of oil. I can’t actually get to the insides of the tank to measure it accurately, and the outside of the tank is enclosed in a ‘bund’ making it even harder.


#6

why?

you can save version as v16 and then you won’t go through a lossy conversion, which any other format will have…

john


#7

Thanks @john_drivenupthewall, but when I opened the 2016 file in 2017, the first screen says that the up conversion prevents it being opened again in the previous version. No, I didn’t test that, just took their word for it.


#8

Sorry, mis-read your reply which clearly says to save as 2016.


#9

Well the tank model alone is 1.745 M^3 which is 1745 liters.
There are techniques to actually measure the none filled vol of tank if you want to go that trouble, I had to do that on one of items for a space mission( It was much smaller). Your model would be more accurate if you increase number of segments. You can use the universal gas law.:grinning:


#10

I have moved forward a bit. I have reverted to the 2017 version and removed some of the internal faces, as in the attached model. But the supports are still separate entities, and there is no join between the space inside the cylinder and the space inside the 4 supports.
Can anyone point me in the next direction?
I think it would be helpful if I could draw a horizontal separating line across the ribs of the cylinder where they join the supports and remove the curved surface between the cylinder and supports, but haven’t found how to do that yet - when I open the component, put a section across the middle of the cylinder so that I can see inside, select the curved surface between the cylinder and support, then try and draw a line across the selected surface, nothing happens.
Oil tank 7.skp (251.8 KB)


#11

There are still some issues with your modeling technique.

You have the Oil Tank Group nested in Component#1 nested in an anonymous Group. The supports are raw geometry in the anonymous outer Group. The Oil Tank’s geometry is all in the Oil Tank group. This makes it impossible for these two sets of geometry to intersect or to be edited at the same time. You need to get all the geometry primitives (edges and faces) into the same Group or Component so that they can interact.

You are also not using SketchUp’s layers appropriately. There are a large number of edges and faces that associate with the Cylinder layer, which has been set as the active layer. To avoid confusing problems with visibility (which can affect your ability to select things) all edges and faces should only associate with Layer0. For that reason you should almost always leave Layer0 as the active layer. Layers in SketchUp do not structure or aggregate anything, they just provide a visibility flag that multiple objects can share.


#12

Thanks again @slbaumgartner. You are right about my modelling technique not being good - I have professionally used a different app for years and am trying to convert.

I have taken the parts and copied them into a new model, so there is only Layer0 and the cylinder definition is gone. I have removed the dividing faces between the cylinder and the supports internally, so there is conceptually only one volume, but I can’t get the entity pane to show the volume field. There are also many unnecessary internal faces, but selecting and deleting those faces causes obvious holes in the surface.

Oil tank2 2.skp (206.7 KB)


#13

SketchUp will never report a volume until the selected object is what SU considers a “solid”, as reported at the top of the Entity Info window. You aren’t there yet!

I know it can be very frustrating to hear this, but your best approach may be to start over and avoid problems by being more careful from the beginning. Often it is actually faster and easier to begin anew than to struggle trying to repair flaws in an existing model. Sometimes the flaws are subtle, entangled, and very hard to fix.

In your specific model, take a look at the attached screenshot for just a few examples of what I can find. This is not an exhaustive analysis, just what I noticed in a couple of minutes of orbiting around your model and checking things.

Notice how the reported locations of vertices have varying x (red axis) values? They are not coplanar, and that is causing SketchUp to preserve faces that you no doubt meant to merge (see those lines crossing the foot?). The edges are close enough to planar that they “bleed” through a face in the display (a known OpenGL limitation), but not close enough for SketchUp to consider them to actually lie on or cut the face. That is what is causing the mysterious disappearance of more than what you expected: you are actually selecting the whole face, not what visually looks like a subface. The same thing happens on most of the faces of the other feet. Also, notice the little hole between the tank and the foot. It isn’t obvious why this one foot ended up different from the others, but it is!


#14

Thanks very much Steve @slbaumgartner. I appreciate your specific help and the general suggestion to start anew.
One support foot is different because they were all actually drawn individually.
I created the cylinder first by drawing one edge in profile, then copying it to the other side and joining them with a couple of arcs, then using follow-me to create the cylinder. I got it to report a volume so that I knew it was complete.
Then I created the bottom of the 4 support feet and pulled them up into the cylinder (getting different heights since this was manual). Then I joined the ends of the support feet to the bulge of the cylinder and pulled them in again, and this one was not pulled in enough.
The initial edge of the cylinder must be straight to ensure all the parts finish up parallel (specifically the bottom of the feet).
No what I have created this model, I can measure the angle of the sides of the foot support, and their side length, so maybe I could create a single foot support first (a block with a flat top, trapezium shaped), then make 3 copies in the correct place, then copy across the original, known good, cylinder - as a set of faces not a component.
Does that sound like a good approach? It assumes that the cylinder ribs are regularly spaced.


#15

There are two ways to avoid getting different heights: when you have done one push-pull, if you double-click a second face the Tool will extrude it by the same distance, and you can also start the pushpull and then move the cursor over to the end of the first one to get an inference snap to the same height.

It sounds like a large part of your problem is creating the sloping sides of the feet. How about this idea: draw the side profile of the foot off to the side of the tank (your choice whether to worry about the top curve or leave it flat for now, a trapezoid. Make sure you are drawing in the same context as the rest of the tank, that is, either explode the tank or open its component for edit first) and pushpull the profile horizontally to the required thickness. Now move copies of the foot to the four required positions on the tank (you can lock the movement to the red axis and use inference snaps to assure exact positioning). Then select everything (triple click) and use the Intersect Faces with…->selection to generate the edges where the feet meet the tank. Finally, open up the tank with a section plane and delete the unwanted interior faces and edges. Your profile doesn’t say whether you have Make or Pro, but if you have Pro you can use the solid tools to simplify the intersection and cleanup process.


#16

The tank component by its self reports as solid and you can get its vol from entity info as I reported. Fortunately you can simply move the supports to separate them from tank so its measurement is correct. In addition I used TIG’S vol. calculator plugin to double check and it reports exactly same as the entity info. So, if you want to improve the reported value some then you need to spend time to correct for the supports. It is ones decision then to decide when good enough is determent of better especially since SU will not give perfect answer any way?

BTW Andrew I noted the red axis from one end of tank to other does not appear to line up with the pole of the sphere’
Have not double checked yet though. and maybe you can care less.


#17

There are two themes crossing through this topic: calculating the volume of the tank, and learning how to model correctly in SketchUp. To be honest, I am really only interested in the latter, as the former will take care of itself once the model is correct.


#18

Agree with you unless one has to meet schedule and cost constraints. I wonder if you were getting paid by a client and they were spending many dollars to make thing perfect vs some they can use ok what would you / they do. What is the definition of correct is subject to discussion also given the " accuracy" of SU>


#19

Priceless advice @slbaumgartner, I would probably have spent hours searching for this type of tip without knowing what to look for.

And your detailed explanation of how to create the feet is also priceless.
I have Make - I am a long way from being proficient enough to use Pro (I have updated my Profile).


#20

My purpose in starting this topic was definitely to learn how to best use SU. As you say, the tank volume will take care of itself.