[PerryPlatypus]

In testing both the stable 1.3 version of OR (and in Carlos' Monogame release) it seems like the checkbox for "Adhesion Proportional to Rain/Snow/Fog" is no longer working correctly. Up until I upgraded to this version (I had a couple month old version), the "Conditions" parameter would not drop below 100% when this box was NOT checked (which is correct behavior). Now, it seems that even with the box not checked, rain and snow still reduce adhesion.

Personally, I have been leaving this box unchecked because I still believe that the way that OR is reducing adhesion in rain and snow is not correct (as I had mentioned in a previous thread: http://www.elvastowe...__1#entry230812

But now it seems OR is forcing the precipitation and fog dependent adhesion regardless of whether the box is checked.

Can someone else confirm this behavior?

[James Ross]

PerryPlatypus, on 23 November 2018 - 11:05 AM, said:

Can someone else confirm this behavior?

I have tested 1.2 and 1.3 and they are behaving the same for me: Options > Simulation > "Advanced adhesion model" determines which model is used. The experimental option "Adhesion proportional to rain/snow/fog" only changes the adhesion level of the advanced model, not which model is used in my testing.

If you want the simple model, in both 1.2 and 1.3, you need to unselect Options > Simulation > "Advanced adhesion model". The defaults for these two options do not appear to have changed either.

[PerryPlatypus]

I DO want the Advanced Adhesion model on, and I have it enabled. I want to disable specifically the "Adhesion proportional to rain/snow/fog" function. But from what I am seeing, unchecking the Proportional to Rain/Snow/Fog box is not actually disabling it. It's as if the Proportional to Rain/Snow/Fog function is locked on, even when the box for it is unchecked. In previous versions of OR, I could run the Advanced Adhesion Model, but have the proportional to Rain/Snow/Fog function off.

Here's how to check: Turn on Advanced Adhesion, uncheck the proportional to rain/snow/fog box. Run an activity in Snow, and use the extended F5 to look at Conditions. Turning on and off snow and/or rain, you can see that the adhesion is still being affected by precip.

[James Ross]

PerryPlatypus, on 23 November 2018 - 01:49 PM, said:

Here's how to check: Turn on Advanced Adhesion, uncheck the proportional to rain/snow/fog box. Run an activity in Snow, and use the extended F5 to look at Conditions. Turning on and off snow and/or rain, you can see that the adhesion is still being affected by precip.

Yes, the adhesion is the same with the experimental proportional option on or off, however, this is the same as in 1.2:

https://james-ross.co.uk/temp/orts_160.png

You'll need to figure out which version you had where this is not the case for us to make progress here.

[PerryPlatypus]

I'm not seeing the item called "Conditions" in your screenshots, which will be the easiest basis of comparison for us to use. With no precip, "Conditions" will show as 100%. With precip, it should drop to some number less than 100% if the Proportional to Rain/Snow/Fog box is checked. (in previous versions, this Conditions parameter would not drop below 100% if the box was unchecked). Also, you may want to try a modern diesel engine to see a significant difference in the Loco Adhesion value (like an ES44AC or similar). If your steam loco's max adhesion even on dry rail is 17%, then you may not even see a difference between the Loco Adhesion percentages.

I will be at my main computer this evening to try to grab some screenshots. :)

[PerryPlatypus]

James,

My apologies, it looks like I may have been wrong about this not being a problem in previous versions. I cannot find a previous version where this issue is fixed. However, the adhesion behavior still seems incorrect on two fronts:

1. What is the point of having an item called "Adhesion proportional to rain/snow/fog" if unchecking it does not actually have the effect that it seems to imply? The only effect I am seeing is that the fog density does not impact adhesion with the box unchecked. Rain and snow seem to act exactly the same in regards to their effect on adhesion, both with that box checked or unchecked. I would expect that unchecking the box should simply make rain and snow no longer have any effect on adhesion (in other words, adhesion would be the same as if running in "clear" weather. Can anyone say for sure what the actual intention of the "Adhesion proportional to rain/snow/fog" box was?

2. I still stand by the fact that the precipitation and fog-dependent parts of the adhesion model are not realistic. As mentioned in the thread that I linked to earlier in this thread, the adhesion reduction that occurs due to rain and snow should not be affecting all locomotives, but should diminish in effect with each passing wheel (such that trailing locomotives are not affected as severely). This is proven by the fact that when it is raining or snowing, we do not see trains going up steep mountain grades suddenly require double the number of locomotives in order to keep operating. Trains routinely ascend Mullan Pass and other steep grades in the western U.S. in heavy snowfall and pouring rain without requiring additional locomotives, but perhaps at a bit reduced speed, or requiring sand.

Also, why is fog having an effect on adhesion? There are lots of situations where fog is present with no ice accumulation on the rail (I would say most of the time in fact). This really deserves a separate setting specifically for ice, rather than having it dependent on fog.

[copperpen]

I have my adhesion factor sliders set to 100% top one and 0% bottom one. If I then check the proportional adhesion box it changes the adhesion factor from Normal to Very Hard. If however I check the Force information box while running with Snow, there is no change to Condition which remains at 40% with the box checked or unchecked and the adhesion factor remains unchanged at 13% for both engine and wagons. So, what exactly is the check box for proportional adhesion actually doing?.

[steamer_ctn]

Some feedback on the questions raised in this thread:

Firstly the Adhesion models have slightly different displays in the HUD (and calculations in OR) depending upon whether it is a steam or diesel/electric locomotive.

In terms of the "best reference" value to use, it is probably better to look at the Loco Adhesion value as this gives a value that can be directly related to the coefficient of friction (CoF). For example, a value of 33% is equal to a CoF of 0.33, which is the generally accepted value for dry rail conditions.

The "Adhesion proportional to rain/snow/fog" option has the following impacts:
I) Clear Weather - Variation in Fog conditions will cause changes in the CoFii) Rain Weather - Variation in Precipitation conditions will cause changes in the CoF
Both of these variations have a "magic" formula to facilitate the adjustments, and naturally the fog/precipitation conditions need to be changing, and appropriate weather conditions set, for there to be a change in the CoF.
At the moment the OR code considers each locomotive/wagon as though it is the first car, so no difference in CoF is allowed for with trailing locomotives.
Many scholarly articles suggest that light applications of water (ie Fog) can be worse then heavy rain in terms of the impact on the CoF.

[PerryPlatypus]

Thanks Peter, I have never noticed the difference in the HUD between diesel/electric and steam, that makes sense.

I'll also retract my earlier statement, and I now agree with you that Loco Adhesion is a better basis for comparison.

I have been using user-generated values for adhesion in order to get realistic tractive effort on big AC diesels like SD70ACe's and ES44AC's. The starting tractive effort of a SD70ACe is 191,000 lbs, with the weight of the loco being 408,000 lbs. As far as I know, this means an adhesion of 46.8% starting on dry rail. I made an Excel spreadsheet to calculate Curtius-Kniffler numbers in order to get the correct starting and "continuous" tractive effort, so my TE curve in OR matches the prototype (on dry rail conditions). I believe these values are trustworthy, as using them, it results in train physics performing VERY close to the anecdotal descriptions I've received from real engineers on Montana Rail Link.

While changing the fog density fog does seem to gradually affect adhesion with the Advanced Model turned on, I have tried to vary the rain and snow intensities up and down, and I see no change until they are completely off.

"At the moment the OR code considers each locomotive/wagon as though it is the first car, so no difference in CoF is allowed for with trailing locomotives."

I think this is a HUGE flaw in terms of achieving realistic physics. For all of the other things that OR is calculating, include wind resistance, curve resistance, tunnel drag forces, etc. etc., this seems like it could have a major overall effect on train physics, especially when taking into account what I said as far as trailing axles and locomotives would not encounter as severe of moisture as the front axles on the train. One article I read indicates that the newest GE and EMD locomotives are intentionally constructed such that slightly more weight is put on the rear truck, with the assumption being that the front truck will help to clear debris and/or water off the rail.

Obviously the most difficult thing with this will be trying to determine exactly how many passing wheels on a consist that it takes to clear the rail of a certain amount of rain, or snow, or ice (in other words, how quickly the effect of the precip and/or fog should diminish in respect to adhesion with each passing axle and/or car)

In absence of proven data on this, we may need to resort to anecdotal information from real world train engineers. I can possibly get some information from friends of mine who have firsthand experience driving trains up mountain grades in adverse weather conditions, and we could roughly back-calculate some factors, if there is any interest in this from the Open Rails development team.

[steamer_ctn]

PerryPlatypus, on 26 November 2018 - 11:53 AM, said:

I think this is a HUGE flaw in terms of achieving realistic physics.

I am happy to have a look at this, but whilst anecdotal information is useful to give us a gut feel as to how the physics might react, I would need some more scholarly information that could be "easily" adapted to provide OR with an appropriate physics algorithm.