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Some experiments with water pressure and material strength


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This will be a bit quick and semi-scientific since I need to make breakfast for the kiddo here shortly : )

I think it's understood that granite is stronger than sandstone when holding liquids but I wanted to put some more precise measurements behind it.  One observation I had is that the amount of water a cell contains increases by ~+10kg per tile depth (e.g, the bottom layer of a 2-tile deep pool contains 1010kg of water)

In debug mode I spawned single column holding containers out of standstone and granite.  

The TL;DR - Sandstone started to take damage in the bottom cell once the cell above it held 1050kg of water.  Granite, 1160kg.

I did not do any tests using wider containers, thicker walls, other materials or "dropping" water at this time.  

I attached a picture just so you can see the approach; ignore the scribbled out bits in the middle.  Left is granite, right is sandstone (Since drained).  The bottom tile is at 1171kg which is why I expect the side is cracking as well (the tile next to the cracking side is 1161kg).

I'll try with wider and multi-layer containers when I get time.

Enjoy,

 

2017-07-02_LI.jpg

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Speaking of water pressure, has anyone else noticed that building a tile in water seems to greatly increase the likelihood of it structurally failing. I've had several instances of trying to seal up geysers and create waterlocks with abyssalite where even the abyssalite starts failing. The waterlock even had 2 block thickness of abyssalite.

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6 minutes ago, Whispershade said:

Speaking of water pressure, has anyone else noticed that building a tile in water seems to greatly increase the likelihood of it structurally failing. I've had several instances of trying to seal up geysers and create waterlocks with abyssalite where even the abyssalite starts failing. The waterlock even had 2 block thickness of abyssalite.

yeah, i have. i built a wall, 2 block thick between a geyser and my waste water storage, it broke randomly not always where it was highest pressure either. i had to make the wall 3 block thick before it held up, i think its ridicules that its needed, if there is pressure from both sides it should remain intact imo. even with 1 block.

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52 minutes ago, Whispershade said:

Speaking of water pressure, has anyone else noticed that building a tile in water seems to greatly increase the likelihood of it structurally failing. I've had several instances of trying to seal up geysers and create waterlocks with abyssalite where even the abyssalite starts failing. The waterlock even had 2 block thickness of abyssalite.

When you build a tile, it displaces the gas or liquid that was originally in that place. For liquids it means local pressure will rise a lot for a few physics ticks before the liquid spreads into surrounding tiles.

Water in ONI seems to fall very fast but pressure waves in it spread about as slow as in gases.

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1 hour ago, Kasuha said:

When you build a tile, it displaces the gas or liquid that was originally in that place. For liquids it means local pressure will rise a lot for a few physics ticks before the liquid spreads into surrounding tiles.

Water in ONI seems to fall very fast but pressure waves in it spread about as slow as in gases.

In the case of sealing the geyser and building a bridge between ladder segments in a lake (and rebuilding a waterlock I foolishly made out of igneous rock), I suspected strongly it was an issue of displacement. But I am curious about another waterlock I had, does frequent dupe traffic through a pool of water affect water displacement? I was seeing a lot of movement of the waterline and the abyssalite was starting to fail when I switched to a different airlock scheme. Thinking about it, I guess co2 release might have been an instigating factor.

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Few more observations and probably all I can get to today.  This is all using single-wall constructed tiles.

  • Sandstone hardness is 10; tiles break at 1050kg liquid pressure.  Max safe depth is 5 tiles.
  • Igneous Rock hardness is 25; tiles break at 1100kg liquid pressure.  Max safe depth is 10 tiles.
  • Granite hardness is 80; tiles break at 1150kg liquid pressure.  Max safe depth is 15 tiles.

Liquid is a bit unpredictable; it compresses down and more slowly will uncompress upward.  The "maximum safe depth" above is to ensure the pressure never goes above the given liquid pressure once it reaches equilibrium.  I was able to achieve one tile higher than this but it depends on how much liquid is in there and eventually is distributed downwards as part of compression so isn't really safe unless you use controlled methods to input it (a liquid pressure switch connected to a pump may be sufficient if pumped slowly enough)

Notes:

  • Width of the container doesn't have any effect AFAIKT
  • Falling water is unpredictable; it doesn't have impact damage per-se but local pressures can get temporarily quite high and I believe this is why we see damage incurred due to falling water.  Safest would be to pump water in; when dropping water constructing 3 wide and then deconstructing should be safe.  
  • Hydro switch reads slightly different than the tile it is in, likely due to differences in rounding?  (Hydro:1149.2,Tile 1149.1)
  • There doesn't seem to be a good correlation between material hardness and tile strength, other than harder materials are stronger.  Does anyone know how to read the strength of the constructed tile?  I'm curious if it is different than the material itself.  
  • An over-pressure tile definitely prefers to break a tile below it first.  From there it seems to prefer breaking tiles to the left, then the right.  I never saw a case where an over-pressure tile caused more than one tile to crack, but did not test extensively nor test with multiple material types.
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Double the walls simply doubles the holding pressure the block is capable of (for the same material anyway - I'll try later with mixed materials.  Guessing it is a simple sum).  So you can hold 1100kg of water back with 2xsandstone base tiles.

Also corners aren't needed - forces don't move diagonally.  Below are the minimum "safe" sandstone-based containers that will survive a reasonable* level of flooding.  You can make them as wide as you want.

2017-07-02 (2).png

*No guarantees that the physics engine won't generate temporarily high pressures under some conditions ; -).  Three thick (or doors) is the only way to be sure, for now.  

I'm curious if there are mechanical ways to limit pressure - something like a zig-zag channel - to allow us to safely flood areas since pumping is so slow.  For another day!

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Pressure:

I did some experiments just on the water pressurization, in neutronium chambers. It looks like the best fit for pressurization is the following:

  • Each liquid has a standard cell mass (S). For water, 1000 kg. For polluted water, 800 kg.
  • The capacity of a cell, C, is based on the mass of liquid on the cell above, A: C = 1.01 * MAX(A, 0.99*S)
  • This can be expressed in terms of depth (D) as follows, assuming that the top tile has less than 0.99S: (1.01^(D-1))*0.99*S

You can basically consider this to mean that a cell's capacity is 1% greater than the mass of the cell above it, with a minimum capacity of just under the standard mass. So the rule of thumb for +10 kg per cell is pretty close, but it'll actually be a bit more than that. And a bit more than +8 kg per cell with polluted water.

I repeated this with polluted water and molten gold (because it has really different properties), and they both fit the same model, although gold was off by 1-2 kg for reasons I couldn't figure out (maybe the factor is not quite 1.01, but something like 1.00981? That seems weird, though).

Pressure Capacity:

As for pressure damage, I tested Sedimentary Rock, Sandstone, Granite, and Abyssalite; with water, I got 1020 to break Sedimentary Rock, 1050 for Sandstone, 1150 for Granite, and 1200 for Abyssalite. Insulated tiles behaved exactly the same, so mass is clearly not a consideration for the tiles. With two tiles, the amount over 1000 seemed to double. With 3 tiles, no amount of liquid seemed to be able to break it. For polluted water, they broke at 820, 850, 950, and 1000 -- so the same amounts over the standard cell mass.

Interestingly, as soon as pressure damage occurs, it starts leaking; this can bring it below the threshold for damage (Sedimentary Rock restabilized after one "drop" sound with 1019.7 kg). With multiple tiles, though, it didn't leak, so it could never stabilize.

So what is the relationship between hardness and pressure capacity? It's certainly not linear (2->20, 10->50, 80->150, 200->200). GrimerX's test with Igneous means its hardness of 25 results in 100 kg. I also tested with Obsidian (hardness 50), which was also 100. So clearly hardness is not used, but instead there are tiers with manually-defined resistances. Testing mixed materials, the pressure resistance of them is just added.

I tried building gas-permeable tiles out of it and found that those do not break due to pressure damage at all.

Expressing the pressure formula in terms of capacity, this is the depth that will match a particular capacity K:

D = ( log[ ((K/S) + 1) / 0.99) ] / log[1.01] ) + 1

Recommendations:

So to turn the formula into practical recommendations...

It definitely seems like the easiest approach is just to use 3-thick, or gas permeable tiles, or airlocks. Now that it's clear 2-tile just doubles resistance, 3-tile doesn't seem any less an exploit than airlocks and gas permeable tiles to me.

If you do want to use thinner walls for whatever reason, using the depth formula from above, here are critical depths for water and polluted water (ignoring sedimentary rock capacities because they suck)

  • Sandstone: 50 kg capacity, depth 6 water, depth 8 polluted
  • Double Sandstone / Igneous Rock / Obsidian: 100 kg capacity, depth 11 water, depth 13 polluted
  • Granite: 150 kg capacity, depth 16 water, depth 19 polluted
  • Abyssalite: 200 kg capacity, depth 20 water, depth 24 polluted
  • Double granite: 300 kg capacity, depth 28 water, depth 34 polluted
  • Double abyssalite: 400 kg capacity, depth 35 water, depth 42 polluted

Edit: However, I think there are lots of pressurization bugs that also severely limit this calculated approach. For example, liquids can get overpressurized when they don't have cells to expand into (because they're being held by gas, for example). Once this type of overpressurization occurs it can quickly run out of control and over the capacity of the material.

 

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