pitch and DEMON

arl85 · 06-23-07, 12:08 PM

hi! Strange question: if in FFG I set only the pitch and I don't touch the throttle, will the DEMON show increasing speed? the propeller shouldn't turn quickier so I think the DEMON will not show the increased speed. I can't test this behavior, because I have only one pc...

thanks in advance

Dr.Sid · 06-23-07, 03:23 PM

DEMON always shows actual speed, no shaft RPM as it should. It is simply not simulated well enough.

arl85 · 06-25-07, 03:38 PM

you're right.
I make some test using the ffg towed array. so i can see my own noise and i can use demon on it.well,it show my right speed but the amount of noise it's related only to the propeller speed...
so, if you set the pitch to the max and the engine to ahead 1/3 you are able to obtain a speed of 11 knots but the towed array show me the same noise of when i go to 5 knots! you don't cavitate...
it's a bug? or is "well modelled"? noise it's related to speed or to propeller rpm?

thanks

Dr.Sid · 06-25-07, 04:55 PM

Noise is related to million things. Demon works with propeller noise, and that should depend on power which propeller transfers onto the water. Accelerating boat will make more noise, boat steady at high speed too.

There is also water flow noise which depend on speed only, but that is quite uniform noise with no modulation which DEMON could analyze.

DW uses most simple simulations, even so many people find it too difficult (not on this forum I hope !).

Bubblehead Nuke · 06-25-07, 08:36 PM

Quote:

Originally Posted by Dr.Sid

Noise is related to million things. Demon works with propeller noise, and that should depend on power which propeller transfers onto the water. Accelerating boat will make more noise, boat steady at high speed too.

Um, Demon works by displaying a bladerate based on repeditive harmonics. Thus if the RPM is constant then the bladerate shown will be constant regardless of the pitch the blades are set at.

They must have snuck this in the last patch, I know in testing previously they did not model DEMON correctly for a gas turbine ship. This was one of my petpeeves that I was complaining about when I first started posting here. What used to happen was demon showed a bladerate proportional to ship speed that did to take into account blade pitch.

Here was my post on the matter

http://www.subsim.com/radioroom/showthread.php?t=92950

arl85 · 06-26-07, 02:14 AM

Quote:

Originally Posted by arl85

so, if you set the pitch to the max and the engine to ahead 1/3 you are able to obtain a speed of 11 knots but the towed array show me the same noise of when i go to 5 knots!

so changing the pitch will raise my speed...but since propeller rotate at previous speed the noise generated will be the same?

I think it should not be in this way...the TA should show noise increasing...or not? :hmm:

Quote:

Originally Posted by Bubblehead Nuke

Um, Demon works by displaying a bladerate based on repeditive harmonics. Thus if the RPM is constant then the bladerate shown will be constant regardless of the pitch the blades are set at.[...]What used to happen was demon showed a bladerate proportional to ship speed that did to take into account blade pitch.

I think so...but using the TA of FFG to analyze my own noise i can only see the speed, not the bladerate...

Dr.Sid · 06-26-07, 07:58 AM

If you only change pitch, noise should be louder, but it will be modulated by higher frequency (by shaft rotation with its harmonisc). Whole my post was about INTENSITY of the sound, not modualating frequency. Frequency is clearly shaft rotation speed.

But in DW demon is not shaft realated. It depends on speed alone. Which is incorect, of course. Whole DEMON is not correctly modeled at all. Whole idea that number of lines corresponds to number of blades is wrong. There was some posts about DEMON which linked to some good IRL info. Try some searching in thread titles (look for DEMON).

arl85 · 06-27-07, 06:24 AM

Quote:

Originally Posted by Dr.Sid

If you only change pitch, noise should be louder, but it will be modulated by higher frequency (by shaft rotation with its harmonisc). Whole my post was about INTENSITY of the sound, not modualating frequency. Frequency is clearly shaft rotation speed.

But in DW demon is not shaft realated. It depends on speed alone. Which is incorect, of course. Whole DEMON is not correctly modeled at all. Whole idea that number of lines corresponds to number of blades is wrong. There was some posts about DEMON which linked to some good IRL info. Try some searching in thread titles (look for DEMON).

thanks,dr.sid. i've understood about demon, but also the noise showed by towed array is wrong, because if change only pitch and speed increases, the noise remain the same...so it appears that changing pitch i can obtain higher speed without cavitating and this is wrong, or not?

Dr.Sid · 06-27-07, 11:43 AM

Whole ship noise, which is displayed by towed array (broadband), consists mainly from screw noise and water flow noise. Water flow noise is independent of screw speed or pitch. It simply gets louder as ship goes faster (similar to air noise in car).
Screw noise depends on force transfered to water, which is simmilar to engine noise in car. If you accelerate or go fast (which means you must constantly push the boat against the water) there will be lots of noise.

In DW ship noise is dependent only on actual speed and cavitation. If you go faster it should get louder. What speeds are you talking about ?

Also FFG in DW cavitates at speeds under 5 kts. How fast did you make it go without cavitation ?

arl85 · 06-27-07, 04:04 PM

Quote:

Originally Posted by arl85

so, if you set the pitch to the max and the engine to ahead 1/3 you are able to obtain a speed of 11 knots but the towed array show me the same noise of when i go to 5 knots! you don't cavitate...

i'm quoting my second post.

well, i think i don't cavitate because at 5 knots the noise is very low (snr=40).when i set engine ahead 2/3, noise became louder (snr=60) and speed raises to 10 knots.but if i set engine to 1/3 and pitch to max i obtain a speed of 11 knots but the same noise of when i go to 5 knots. also (and this is the strangest thing for me) if i set engine to all stop and pitch to max i'm able to obtain a speed of 11 knots (and the same noise, snr=40)

i hope i was able to explain the problem clearly

Dr.Sid · 06-27-07, 05:33 PM

You can easily check cavitation by 3d view. Screw either makes bubbles or not.

It's pretty funny anyway. I never tried to manipulate screw pitch. I control all with schortcuts

Have to try that.

Dr.Sid · 06-27-07, 05:59 PM

Hm .. with LWAMI mod I get about 40 SNR with no cavitation and 60 SNR with cavitation. I really think it should get more complex.

I tried to change screw pitch but I really got no reasonable behavior from that. It's complete mystery to me.

BUT ! FFG measures SNR in great way ! Some time ago I was trying to actually measure DW's sound propagation model, to draw transmission loss diagrams. But I was doing it in sub, and subs don't have such nice SNR display, I got no reasonable data and I gave it up.

I did some simple tests in FFG now and it will work ! So after I get some more time (will take few hours I guess), expect new insight into DW's sound propagation model.

06-23-07, 12:08 PM	#1
arl85 Swabbie Join Date: May 2007 Posts: 14 Downloads: 4 Uploads: 0	pitch and DEMON hi! Strange question: if in FFG I set only the pitch and I don't touch the throttle, will the DEMON show increasing speed? the propeller shouldn't turn quickier so I think the DEMON will not show the increased speed. I can't test this behavior, because I have only one pc... thanks in advance

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06-23-07, 03:23 PM	#2
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	DEMON always shows actual speed, no shaft RPM as it should. It is simply not simulated well enough.

06-25-07, 03:38 PM	#3
arl85 Swabbie Join Date: May 2007 Posts: 14 Downloads: 4 Uploads: 0	you're right. I make some test using the ffg towed array. so i can see my own noise and i can use demon on it.well,it show my right speed but the amount of noise it's related only to the propeller speed... so, if you set the pitch to the max and the engine to ahead 1/3 you are able to obtain a speed of 11 knots but the towed array show me the same noise of when i go to 5 knots! you don't cavitate... it's a bug? or is "well modelled"? noise it's related to speed or to propeller rpm? thanks

06-25-07, 04:55 PM	#4
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	Noise is related to million things. Demon works with propeller noise, and that should depend on power which propeller transfers onto the water. Accelerating boat will make more noise, boat steady at high speed too. There is also water flow noise which depend on speed only, but that is quite uniform noise with no modulation which DEMON could analyze. DW uses most simple simulations, even so many people find it too difficult (not on this forum I hope !).

06-26-07, 07:58 AM	#7
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	If you only change pitch, noise should be louder, but it will be modulated by higher frequency (by shaft rotation with its harmonisc). Whole my post was about INTENSITY of the sound, not modualating frequency. Frequency is clearly shaft rotation speed. But in DW demon is not shaft realated. It depends on speed alone. Which is incorect, of course. Whole DEMON is not correctly modeled at all. Whole idea that number of lines corresponds to number of blades is wrong. There was some posts about DEMON which linked to some good IRL info. Try some searching in thread titles (look for DEMON).

06-27-07, 11:43 AM	#9
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	Whole ship noise, which is displayed by towed array (broadband), consists mainly from screw noise and water flow noise. Water flow noise is independent of screw speed or pitch. It simply gets louder as ship goes faster (similar to air noise in car). Screw noise depends on force transfered to water, which is simmilar to engine noise in car. If you accelerate or go fast (which means you must constantly push the boat against the water) there will be lots of noise. In DW ship noise is dependent only on actual speed and cavitation. If you go faster it should get louder. What speeds are you talking about ? Also FFG in DW cavitates at speeds under 5 kts. How fast did you make it go without cavitation ?

06-27-07, 05:33 PM	#11
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	You can easily check cavitation by 3d view. Screw either makes bubbles or not. It's pretty funny anyway. I never tried to manipulate screw pitch. I control all with schortcuts Have to try that.

06-27-07, 05:59 PM	#12
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	Hm .. with LWAMI mod I get about 40 SNR with no cavitation and 60 SNR with cavitation. I really think it should get more complex. I tried to change screw pitch but I really got no reasonable behavior from that. It's complete mystery to me. BUT ! FFG measures SNR in great way ! Some time ago I was trying to actually measure DW's sound propagation model, to draw transmission loss diagrams. But I was doing it in sub, and subs don't have such nice SNR display, I got no reasonable data and I gave it up. I did some simple tests in FFG now and it will work ! So after I get some more time (will take few hours I guess), expect new insight into DW's sound propagation model.