curves and straight lines .

[the bloody clark]

Ok so as an engineer if you were to choose between constructing an object made up of straight lines ( cube, cuboid, etc.. ) or constructing an object that is made up of curves ( cylinder, sphere, etc .. ) which one would be easier to do and less consuming to the materials ?
if the design you're making requires more balance " taken into consideration that the balance is increased by increasing the width of the base of an object or by lowering the center of gravity " so if the design is half a cylinder would it be more functional to increase the length of the radius or leave the radius as it is and put 2 blocks in the shape of a cuboid beneath the semi-cylinder without increasing the radius making the center of gravity lower than the design where is the radius increased as the center of gravity is at a distance calculated by the rule 4r/3π and which one will be easier ?

 

[3DDave]

Step one in solving engineering problems is to develop a clear problem statement. Universally, a picture is worth a thousand words.

 

[the bloody clark]

" That's what I mean by supporting the semi-cylinder with two blocks in the form of cuboid underneath

 

[dik]

Curved can be a problem, if you have 'cubic' furniture... can also have problems if curved in elevation.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[the bloody clark]

but why the curve makes a problem ?
" Actually I need a scientific base so I can put it in my research paper "

 

[3DDave]

"Ok so as an engineer if you were to choose between constructing an object made up of straight lines ( cube, cuboid, etc.. ) or constructing an object that is made up of curves ( cylinder, sphere, etc .. ) which one would be easier to do and less consuming to the materials ?"

How does that picture relate to the question? How is balance evaluated? What forces are applied?

If that shape was in orbit no amount of weight would balance it, regardless of shape.

What equations will you use to make the balance evaluation? Have you built a simple model out of cardboard?

 

[dik]

Not efficient space... about 40 years back one of my aquaintences built a geodetic dome... furniture didn't fit very well and left a lot of space between the back of it and the wall. A fridge could be 2' from the wall.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SWComposites]

sigh.
what is this "object" supposed to do? design goals and requirements? is it made on Earth or on the moon? etc........
a building doesn't really care where the "center of gravity" is.
generally things are easier built using straight stuff.
lower material might be curved structure (but might not meet other requirements).

the FIRST thing in an engineering exercise is to full define and understand the requirements.

 

[the bloody clark]

let me clarify, I'm working on a project where I'm supposed to make a prototype for a tunnel made up of recycled materials that can withstand load up to 15kg, and its maximum deflection shouldn't exceed 1 cm so the only forces acting on the prototype will be the weight the length of the prototype is 56cm width is equal to 23 cm and the height is 11.5cm as it is made in a semi-circular shape since that I need to increase the height without increasing the width so I decided to add two cuboid shaped blocks beneath the tunnel with width of 3 height of 4 and length of 56 in order to do that I have to mention a scientific base as for why am I doing this so I'm asking if it's better to do that or should I start all over again and increase the radius of the semi-circle from the beginning given the fact that I have almost no time and I need to finish that as quick as possible
n.b : I'm a secondary school student 'grade 10' so pardon the way that I explain the topic with .

 

[IRstuff]

Take a look at the cross-section of a classical Gothic cathedral. Since you've apparently been procrastinating, I've even included one. Note the center has a semicircular ceiling that distributes the load downward onto the vertical inner walls. The roof is not structural, but it would be like your test weight, The side structures keep the vertical walls from buckling outward from its vertical load.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[3DDave]

Getting so close.

The first scientific step is that 15 kg isn't a force. The force is 15 kg in a 9.8m/s^2 acceleration from gravity = 147 Newtons.

Then more questions -

How is the load applied? Is it a blanket of sand or a brick?
Is there a fixed minimum interior dimension?
Is there a fixed maximum exterior dimension?
Is there a prohibition of having a floor?

Increasing the radius means the curvature is lower so the tunnel will also be lower.

Setting this out on a piece of paper full sized will help you a lot. MS Paint won't.

 

[the bloody clark]

the load will be hung from the middle point, it's going to be bricks .
the minimum height is to be 12cm, minimum length is to be 56cm, minimum area of cross section is 288cm^2
it can have a floor .
the point is is it better to support it with the 2 blocks or should I increase the radius ?

 

[3DDave]

It's better to have a floor to tie the two edges from spreading. After that it is less important what spacer is used. You can experiment cheaply with paper towel tubes cut to form the arch and either glued along the edges to a floor or left free. Takes about 10 minutes unless too much air-drying glue (PVA glue, also called "white glue") is used.

 

[BAretired]

I don't think it makes much difference. Personally, I prefer the half ellipse, but unless you are super good model builders, you probably couldn't tell one from the other.

 

[Just Some Nerd]

Kinda nice to see someone in grade 10 posting here



----------------------------------------------------------------------

Why yes, I do in fact have no idea what I'm talking about

 

[BAretired]

if the design you're making requires more balance " taken into consideration that the balance is increased by increasing the width of the base of an object or by lowering the center of gravity " so if the design is half a cylinder would it be more functional to increase the length of the radius or leave the radius as it is and put 2 blocks in the shape of a cuboid beneath the semi-cylinder without increasing the radius making the center of gravity lower than the design where is the radius increased as the center of gravity is at a distance calculated by the rule 4r/3π and which one will be easier ?

Given only these options, I would probably use two cuboids.

let me clarify, I'm working on a project where I'm supposed to make a prototype for a tunnel made up of recycled materials that can withstand load up to 15kg, and its maximum deflection shouldn't exceed 1 cm so the only forces acting on the prototype will be the weight the length of the prototype is 56cm width is equal to 23 cm and the height is 11.5cm as it is made in a semi-circular shape since that I need to increase the height without increasing the width so I decided to add two cuboid shaped blocks beneath the tunnel with width of 3 height of 4 and length of 56 in order to do that I have to mention a scientific base as for why am I doing this so I'm asking if it's better to do that or should I start all over again and increase the radius of the semi-circle from the beginning given the fact that I have almost no time and I need to finish that as quick as possible
n.b : I'm a secondary school student 'grade 10' so pardon the way that I explain the topic with .

Scientific basis? One of the conditions of the assignment was that you could not increase the width. In any case, one good reason is that the actual structure may not have enough space to increase the width (we don't know that).

the load will be hung from the middle point, it's going to be bricks .
the minimum height is to be 12cm, minimum length is to be 56cm, minimum area of cross section is 288cm^2.
it can have a floor .
the point is is it better to support it with the 2 blocks or should I increase the radius ?

Increasing the radius is not an option according to your first post; but in any case, it gives the tunnel a larger footprint, and for that reason, is not a good choice because we must assume that the additional space is not available.

 

[BAretired]

Looks like the OP has abandoned the thread...kids nowadays!

Straight lines or curves? Straight lines would be easier to build in the configuration A-B-C-D-E shown below, easier than a semicircle. The dashed red circle indicates a 24'-0" diameter circle for comparison.

The test load of 15kg, or a force of about 150N acts downward at point C. Dashed blue lines C-A and C-E are vectors showing how the test load gets to the foundation, but bending moments at points B and D would need to be resisted, possibly using plywood or light gauge steel gusset plates. An easier and more economical configuration would be A-C-E, omitting points B and D, but it's unlikely that would be acceptable, as it reduces the tunnel headroom considerably.