[steamer_ctn]

To provide some visibility on OR configuration information for diesels (ie what information that OR is using to calculate the performance of the locomotive), I have added some adhesion diagnostic information that will appear in the LOG file if "Verbose ENG/WAG configuration messages" is selected in the DataLogger TAB.

[R H Steele]

Excellent, much appreciated! http://www.elvastower.com/forums/public/style_emoticons/default/sign_thank_you.gif

[DirtyRam]

R H Steele, on 02 August 2021 - 12:36 PM, said:

Excellent, much appreciated! http://www.elvastower.com/forums/public/style_emoticons/default/sign_thank_you.gif

Yes sir, I concur.

[joe_star]

I decided to post this here as it seems like the latest topic on the subject (rather than starting a new thread)

I started toying with the Curtius-Kniffler Adhesion parameter for a steam locomotive that I am working on, mainly because the standard Curtius seems to have the locomotive glued to track and no wheel slip even on grade and poor conditions (nothing close to prototypical).

Starting with just the default C-K values, I get a perfect match on adhesion for dry conditions. However Wet (and Snow) did not match up with expectation from the standard C-K equations for Wet (I could not find any definitive coefficients for Snow/Ice but literature seems to state icy conditions would be less than wet)

I tried to derive the weighting factor that is being applied for rain and snow based on what OR reported adhesion in the simulator was at rest and got the following factors:-

With Adhesion proportional to rain/snow/fog checked
Dry: 1.0
Wet: 0.55
Snow: 0.6

With Adhesion proportional to rain/snow/fog unchecked
Dry: 1.0
Wet: 0.81
Snow: 0.6

I took the measurements above with 0 weather randomization, over several cycles just to make sure when proportional adhesion is checked, the values aren't varying. The snow coefficient doesn't seem to vary at all at these conditions, but the rain (wet) difference is huge. It is also less than that of the snow condition, which seems a little counterintuitive (assuming the "snow" condition is supposed to model icy conditions as well - which seems the case when proportional adhesion is unchecked). The original "wet" C-K gives around half the value of friction vs "dry" rail, of which all the conditions in OR seem to apply a weighting factor higher than that.

I would like to know if there is any explanation that I am perhaps missing out on here, and anyone familiar with the model and history can elaborate a little on this.

Also, and I am sure this has been discussed before, why are the conditions modeled via a weighting factor that applies to the entire equation? Would it not be more accurate to apply the conditions weighting factor only on the "C" parameter, as this is what is changing in the original C-K equation?

[joe_star]

The more I test the more questions come up:-

a) Do helper locomotives use a simple adhesion model? I notice my helper steam locomotive never sees wheel slip and provides continous tractive effort even when the main locomotive is well into wheel slip territory. The net effect is the train does not slide backward (as it should when no tractive effort is being transferred to the rails from both identical locomotives operating at similar regulator/reverser settings)

B) I noticed that when trying to start the train, at times the sanding effect just cuts off, resulting of course in wheel slip and inability to start.. Is this intentional?

Both effects are captured in the video below. You can see initially the train is rolling slightly backwards, but as traction is applied (with sanding in effect) crawls to a halt, at which point the adhesion factor drops to un-sanded levels and wheel slip initiates. Also can be seen that the helper locomotive (right at the back) is unaffected by the wheel slip, continously providing full tractive effort throughout.

https://youtu.be/x3kSN3L8iuI

And since I didnt mention it before, am using OR NYMG 1.4-44 Rev109.2

[Laci1959]

Quote

I noticed that when trying to start the train, at times the sanding effect just cuts off, resulting of course in wheel slip and inability to start.. Is this intentional?

There are locomotives that have an automatic sandbox, but not all of them.
Maybe it's powered by AntiSlip (1).

[joe_star]

Laci1959, on 08 November 2021 - 11:25 PM, said:

There are locomotives that have an automatic sandbox, but not all of them.
Maybe it's powered by AntiSlip (1).

It's a steam locomotive, no antislip statement in the eng file.

Sanding is not being switched off during the transition, infact you can see sander is still on throughout. However the moment the locomotive grinds to a halt, the cof drops to unsanded levels, initiating wheelslip, and then jumps up again to sanded levels when some wheel movement is initiated

It would appear to me that when stationary, sand has no effect on the cof as currently coded, which may have some accuracy to it. Just wondering if this indeed is the intent here

[steamer_ctn]

joe_star, on 08 November 2021 - 06:40 PM, said:

(I could not find any definitive coefficients for Snow/Ice but literature seems to state icy conditions would be less than wet)

Not always. See table 14.1 for example.

Note that dew (light wet conditions) can have a lot lower CoF then wet rail. So it depends upon how much moisture is involved.

So as you have pointed out the main variation with precipitation is the amount of rain, ie light rain will have a lower CoF then heavier rain. From what I have seen with my research there doesn't seem to be a wide variation due to the different types of snow.

Like the rest of OR the adhesion model is representative and does not attempt to model all the variables associated with the calculation of CoF. As can be seen from the table there can be a reasonable spread in CoF values depending upon track conditions, etc.

joe_star, on 08 November 2021 - 08:45 PM, said:

a) Do helper locomotives use a simple adhesion model? I notice my helper steam locomotive never sees wheel slip and provides continous tractive effort even when the main locomotive is well into wheel slip territory. The net effect is the train does not slide backward (as it should when no tractive effort is being transferred to the rails from both identical locomotives operating at similar regulator/reverser settings)

Helper locomotives were not covered by the advanced adhesion calculations.

I have uploaded a patch to the unstable version to correct this. The rear locomotive in your consist should now (hopefully) suffer wheel slip as well. Please confirm.


Strictly speaking the adhesion of the front locomotive will be different to the last locomotive as the wheels of the train tend to "dry the track" out somewhat as they pass over it.

joe_star, on 09 November 2021 - 06:50 PM, said:

It would appear to me that when stationary, sand has no effect on the cof as currently coded, which may have some accuracy to it. Just wondering if this indeed is the intent here

Correct, it doesn't make sense to put a large pile of sand on the tracks if the train is not moving.

I would also wonder whether the driving method of allowing the train to run backwards and then try to get it moving forwards without bringing it to a complete stop is realistic.

[joe_star]

steamer_ctn, on 09 November 2021 - 07:47 PM, said:

Not always. See table 14.1 for example.

Note that dew (light wet conditions) can have a lot lower CoF then wet rail. So it depends upon how much moisture is involved.

So as you have pointed out the main variation with precipitation is the amount of rain, ie light rain will have a lower CoF then heavier rain. From what I have seen with my research there doesn't seem to be a wide variation due to the different types of snow.

Like the rest of OR the adhesion model is representative and does not attempt to model all the variables associated with the calculation of CoF. As can be seen from the table there can be a reasonable spread in CoF values depending upon track conditions, etc.

Thanks for the explanation. I still wonder why the "rain" scenario when "adhesion proportional to rain/snow/fog" is checked vs unchecked have such large variation though. Both seem to be applying to different scenarios. I would assume with weather randomization set to "0" they should give the same outcome.

steamer_ctn, on 09 November 2021 - 07:47 PM, said:

Helper locomotives were not covered by the advanced adhesion calculations.

I have uploaded a patch to the unstable version to correct this. The rear locomotive in your consist should now (hopefully) suffer wheel slip as well. Please confirm.


Strictly speaking the adhesion of the front locomotive will be different to the last locomotive as the wheels of the train tend to "dry the track" out somewhat as they pass over it.

Will test and feedback. Yes you are right, there should be better grip on the rear locomotive (or vice versa in case direction is reversed).

steamer_ctn, on 09 November 2021 - 07:47 PM, said:

Correct, it doesn't make sense to put a large pile of sand on the tracks if the train is not moving.

I would also wonder whether the driving method of allowing the train to run backwards and then try to get it moving forwards without bringing it to a complete stop is realistic.

I actually went watching some wheel slippage videos on Youtube after the fact. Its clear that sand dumping is a big no-no. Will read more into prototypical handling of wheel slippage and see how i fare in OR after this :)

[joe_star]

Reporting back that the helper locomotive now is indeed under the advanced adhesion model,and shows similar characteristics to the main locomotive at starting.

Coming back to the adhesion model, I still am curious why the weather coefficient was applied to the entire C-K equation (A,B,C) when the original C-K equation only the "C" factor really changes with weather conditions. Was this based on additional research perhaps?