Author Topic: Mess with your minds: A wind powered craft going faster than a tail wind speed.  (Read 147345 times)

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Online IanB

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If you disagree post what you think are the correct ones.  I do not make a video without checking multiple times and making sure what I say is correct. I can of course still make mistakes as anyone else.
Looking forward to your results for that problem.

No, I will not. Your education is not my problem.

You are either trolling, getting people to spend their time posting, to see how long you can make it continue. Or you lack sufficient understanding to support any kind of dialog, and lack any capacity to learn.

Either way, you are wasting people's time.
 

Offline electrodacus

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The case with the wheels is a bit different from the prop case, but I think it contains the same difficulty in understanding. As an advantage the basics of mechanics are a bit simpler and less of an approximation. So it may be OK to look again at this simpler picture for the start.

To judge if the equations are correct or not the first thing is to make clear what is meant with P_out and P_net mean and the condition for the vehicle.
For the condition of the vehicle the situation to look at, the most useful case would be the vehicle standing still in the picture and with F_G = F_M to have a stationary case with no acceleration.

So what do P_out and P_net stand for ?

The equations are for the vehicle as the reference so vehicle is considered fixed not moving.
Pout is the output on the Motor wheel. Each of the two wheels is on a different independent medium but the wheels can not move relative to each other as they are connected by the body of the vehicle.

So taking case A.
If you want to take 10W from the front generator wheel then you will end up with a 5N force trying to push vehicle backwards right to left. But you can not have this 5N force unless you also have a 5N equal and opposite force and since this vehicle has just two points of contact the only place that equal and opposite force can be applied is back motor wheel against the Wind treadmill.

Pout will for ideal case contain Pin since all power generated to Generator wheel will be delivered with no losses to Motor wheel but to that power there is also the power that Wind treadmill will apply to motor wheel that will be the same force 5N that already exists at M wheel times the speed of the wind treadmill witch is wind speed minus vehicle speed.
Since Pin has a different direction than Pout the Pnet shows the net value.
If you will want to make calculation of speed maybe plot a speed over time graph then you can select either a speed step or a time step to do the calculation.
Say you select a time step of 1ms then you will calculate the kinetic energy of the vehicle after 1ms of 20W net power applied to vehicle and so vehicle kinetic energy will be whatever it was before + 20mWs (20mJ) and then from kinetic energy you can calculate the new speed of the vehicle at t+1ms and use those new values to calculate the new Pnet and then again add that to existing kinetic energy then again calculate the new speed and this way you can plot a speed vs time graph.


The main point of this 3 example's was to show that when you exceed wind speed the direction for wind treadmill has changed and thus instead of helping you to accelerate it will help you decelerate.
To get around this and ignore the energy storage Derek just decided to reverse the equation and use vehicle speed minus wind speed instead of the correct one.
You can not just change the equation when you exceed wind speed and same equation will need to be used for all 3 cases. If Derek was to test his equation for vehicle below wind speed case A he will notice that result will show vehicle deceleration and that will make no sense as that is not what happens in real world. Blackbird is many times pushed started but that is not needed it can start without being pushed.

Offline Kleinstein

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What does output of the motor wheel mean ? This is not really clear to me.
It that the same as the power needed to supply the motor = the ouput power of the motor ?

For now it is just about the equation, so we don' t need to dicuss the 3 cases. We need to understand the equation first.
 

Offline electrodacus

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What does output of the motor wheel mean ? This is not really clear to me.
It that the same as the power needed to supply the motor = the ouput power of the motor ?

For now it is just about the equation, so we don' t need to dicuss the 3 cases. We need to understand the equation first.

Output at the motor wheel is the input power in the motor from generator wheel plus the power that wind treadmill provide to that same wheel or subtract from the wheel as it is the case at C.
There are just two sources of energy available to vehicle one is the road treadmill and one is the wind treadmill. This is because we are looking in the frame of reference of the vehicle so vehicle is the reference thus is not moving.

You can salve the same problem in multiple way this is just the one I selected mostly based on the fact that people seems to prefer looking at this problem form the vehicle frame of reference and that is how Derek also solved this same problem.
You can look from the ground reference frame where ground / Road treadmill is not moving at 2m/s but vehicle moves forward at 2m/s left to right and in that case the wind treadmill will have moved at 6m/s the wind speed relative to ground/road but it will still be just 4m/s relative to vehicle.


The way I like to look at the problem (I'm aware it may look more complicated) was as ground/road being the reference so vehicle was moving at 2m/s meaning vehicle kinetic energy will already be 0.5 * 10kg * (2m/s)^2 = 20Ws
Then I can imagine a 10W for 1ms of braking power applied so 10mWs of energy removed from vehicle kinetic energy and stored in some imaginary ideal battery then new vehicle kinetic energy will be 19.99Ws
Then if I apply all this 10mWs to the motor wheel the vehicle will gain back the lost kinetic energy 10mWs and be back to where it started 20Ws thus same exact speed but then there is also the wind treadmill that moves at 6m/s relative to ground but just 4m/s relative to vehicle as vehicle already moves in that same direction at 2m/s and so if force on the motor wheel can only be the same 5N there will be an extra 20W for 1ms provided by the wind thus 20mWs so after that 1ms the new kinetic energy for case A will be 20.02Ws so new vehicle speed will be about 2.001m/s

Offline Brumby

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You seemed to have "overlooked" this:

Do you understand that power you take from the wheel will brake the vehicle ?
If you talk about power and taking a power from the wheel then there is no speed change as power is instantaneous contains no time dimension.

Which is it?  You can't have it both ways.

Care to answer?
 

Online bdunham7

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power is instantaneous contains no time dimension.

It doesn't?  Power = Energy/Time.   Joules per second.  Ergs per eon.  Electron-volts per attosecond.   
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Offline Brumby

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Actually, I'll make this easier for you.......

I can talk about an observation of power over a period of time.  I can carry on a conversation talking about that power and the effect it has on a system over a period of time.  I can talk about how that system can change, make logical deductions and express some qualitative descriptions of outcomes - all without using any other terms in my conversation.  There is nothing erroneous in doing so.  There is also validity in such a conversation even if an explicit reference to time is not included, especially if there is reference made to clearly time dependent characteristics - such as "braking" (change in velocity) - and that is consistent with the logic flow of the conversation.

Yes, the term "energy" has a place, but the conversation doesn't need to use it.

I'm just pointing the fact that you do not know what power is and also do not know the difference between power and energy.
You are so hung up about that ... and you couldn't be more wrong.

Sure there isn't a mirror in your way?
 

Offline Brumby

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I can of course still make mistakes as anyone else.
But you can never admit to them when they go against your beliefs and your responses are the worst kind of ignorance.  You introduce contradictions and deny their existence.


You are either trolling, getting people to spend their time posting, to see how long you can make it continue. Or you lack sufficient understanding to support any kind of dialog, and lack any capacity to learn.
Options are:
 1. Dunning-Kruger
 2. Troll

Quote
Either way, you are wasting people's time.
Agreed.
 
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Offline fourfathom

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power is instantaneous contains no time dimension.

It doesn't?  Power = Energy/Time.   Joules per second.  Ergs per eon.  Electron-volts per attosecond.

Speaking an an electronics nerd who skipped Physics, I think of power in Watts.  Watts = Volts * Amps, and there is no time dimension unless you consider that Amps = Coloumbs per second.  But that is a rate, not a duration.  Even Watt-hours is rate, or a quantity, with no particular duration (unless specified).  I look forward to some clarification.

But honestly, trying to fine-tune and correct these equations is fairly pointless when they do not reflect the actual characteristics of these DDWFTTW vehicles.
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Offline msuffidy

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Be even funnier if this could be a warp field solution.
 

Online IanB

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Speaking an an electronics nerd who skipped Physics, I think of power in Watts.  Watts = Volts * Amps, and there is no time dimension unless you consider that Amps = Coloumbs per second.  But that is a rate, not a duration.  Even Watt-hours is rate, or a quantity, with no particular duration (unless specified).  I look forward to some clarification.

The SI system is a bit sneaky, as it defines fundamental dimensions (among others) as length (L), mass (M), time (T) and electric current (I). But electric current implicitly contains time, as it is charge/time. So dimensions containing current will contain a hidden time dimension.

Now voltage has dimensions of (work)/(charge), where work is dimensionally equivalent to energy, and current is (charge)/(time).

So power = voltage x current, and has dimensions of (work)/(charge) x (charge)/(time) = (work)/(time).

Now (work)/(time) is "the rate of doing work", which is the conventional definition of power, so it all lines up.
 

Offline electrodacus

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You seemed to have "overlooked" this:

Do you understand that power you take from the wheel will brake the vehicle ?
If you talk about power and taking a power from the wheel then there is no speed change as power is instantaneous contains no time dimension.

Which is it?  You can't have it both ways.

Care to answer?

Yes I was talking for the vehicle reference frame and in that case vehicle will not move but you need to consider the 10W in that example braking power.
So no matter how you look at things taking power from generator wheel means deceleration and while in vehicle reference frame and while you use just power no specification for time duration you get Net power that will be the output at motor wheel minus the input at the generator wheel.
If that net power is negative while is just a value it means vehicle will decelerate.
I'm fairly bad at explaining but when you use power there is no time involved so you get a net power that can be positive meaning vehicle can accelerate or negative meaning vehicle will decelerate when you add the time step. 

Offline Brumby

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I'm fairly bad at explaining
No kidding.  You are even worse at understanding.

Your entire response completely overlooks the point I was making - and the focus on power and time just shows you are just babbling on, trying to make your argument sound "scientific", but is way short of the mark.


But honestly, trying to fine-tune and correct these equations is fairly pointless when they do not reflect the actual characteristics of these DDWFTTW vehicles any system.

Precisely this.
 

Offline electrodacus

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power is instantaneous contains no time dimension.

It doesn't?  Power = Energy/Time.   Joules per second.  Ergs per eon.  Electron-volts per attosecond.

Power contains no time component just the energy contains time.
Power is measured in Watt while energy is measured in Joules same as Watt second
If I say a power of 10W is applied for 1ms then you have the energy as 10mJ = 10mWs = 0.01Ws
So yes Power = Energy/Time but the part containing time is Energy not Power that is why you divide by time to get the power.
So in this example 10W = 0.01Ws / 0.001s
« Last Edit: December 21, 2021, 03:38:18 am by electrodacus »
 

Online bdunham7

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Power contains no time component just the energy contains time.
Power is measured in Watt while energy is measured in Joules same as Watt second
So yes Power = Energy/Time but the part containing time is Energy not Power that is why you divide by time to get the power.

That's some extraordinarily convoluted babbling, even for you.  Power literally has no definition other than energy per unit time, or rate of energy transfer.  An amount of energy can be stored (as potential energy, like a compressed spring) for an arbitrary amount of time. 
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Offline Brumby

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There seems to be a lot of difficulty working through the maths for the situation when the Blackbird is travelling at wind speed - so let's back away from that for a moment.

How about we put together the equations that describe the system for the Blackbird when it is travelling at, say, half wind speed?

This will require consideration of all the components including wind input, propeller output, wheel motion and whatever power train is in place between wheels and propeller.  ALL things must be considered and nothing can be dismissed out of hand as they are all, very clearly, involved.

If done correctly, then we follow this mathematical model and see where it ends up.



If you can't be bothered to look at this, properly, then you've revealed yourself as a troll.
 

Offline electrodacus

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That's some extraordinarily convoluted babbling, even for you.  Power literally has no definition other than energy per unit time, or rate of energy transfer.  An amount of energy can be stored (as potential energy, like a compressed spring) for an arbitrary amount of time.

There is nothing wrong with that definition if you understand what it means.
I will say that maybe an analogy may be Force vs Impulse where force contains no time component will be similar to Power vs Energy if that helps.
Same as force, power has nothing to do with time. When you add time to force or power then you are talking about impulse or energy.

Online bdunham7

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There is nothing wrong with that definition if you understand what it means.

What definition?  ::)   Where have you 'defined' power other than to say that it has no time dimension?
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Offline electrodacus

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There seems to be a lot of difficulty working through the maths for the situation when the Blackbird is travelling at wind speed - so let's back away from that for a moment.

How about we put together the equations that describe the system for the Blackbird when it is travelling at, say, half wind speed?

This will require consideration of all the components including wind input, propeller output, wheel motion and whatever power train is in place between wheels and propeller.  ALL things must be considered and nothing can be dismissed out of hand as they are all, very clearly, involved.

If done correctly, then we follow this mathematical model and see where it ends up.



If you can't be bothered to look at this, properly, then you've revealed yourself as a troll.

Case A will be about that. It is not half wind speed is 1/3 but it should be a good case where energy storage is ignored as with wheels on solid surface there is no energy storage.

To relay look at blackbird you can not start from half the wind speed you need to start from zero and integrate all stored energy.

If you want me to demonstrate that without energy storage higher than wind speed is not possible then we can use the wheel model the one with two treadmills below case A.
If you are interested how blackbird works and want to look at those equations then you will need to accept pressure differential energy storage.
Since what happens is that wind power is split in two parts for vehicle one part accelerate the vehicle and the other part is transferred from wheel to propeller and then propeller will increase pressure differential with basically increases the available potential energy is if like wind speed has increased.
You need two numbers the ratio between vehicle acceleration and propeller and the propeller efficiency.  In theoretical model you can have this fixed ratios in real life both the ratio of power for propeller and acceleration will be different at each step and propeller efficiency will also be variable.

Offline electrodacus

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There is nothing wrong with that definition if you understand what it means.

What definition?  ::)   Where have you 'defined' power other than to say that it has no time dimension?

I need to say that since you think it has a time dimension.  I was refereeing to the definition you provided.
Power is just the rate at which energy is converted to another form so it is not containing time. The thing that contains time is energy.

So when I say 10W of braking power and I do not mention any time interval for witch this power is applied then time is not involved at all and no work it is being done.
You may know speed as in case A 2m/s and you can calculate force 5N but that is about all you can know. You can not say about any changes to vehicle speed or kinetic energy as time is not mentioned anywhere.
As soon as I say the 10W is applied for 1ms then you have the time and also the energy 0.01Ws and thus you can calculate what happens to vehicle over that time period including change in kinetic energy and speed.
To me it just seems you do not see power for what it is and it just seems you confuse that with Energy.

Online bdunham7

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Power is just the rate at which energy is converted to another form so it is not containing time.

 |O

Alright, can you define the term 'rate' then?
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Offline electrodacus

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Power is just the rate at which energy is converted to another form so it is not containing time.

 |O

Alright, can you define the term 'rate' then?

The word rate should be self explanatory not sure if I can define that better for you but it has nothing to do with time.

I can give you two examples
10W applied for 1ms is not the same as 10W applied for 5s

First case      10W for 1ms means 0.01Ws
Second case 10W for 5s    means 50Ws
Notice that without mentioning time you do not know how much work you can do with a power of 10W.
So if I say a brake power of 10W was applied to vehicle your only information is that vehicle will slow down at that rate of 10W but that is all you know.
If I say a brake energy of 10Ws was applied then you know the new speed of the vehicle since something happened, the kinetic energy was reduced by 10Ws

If you understand something else or do not agree with my examples let me know. But from your earlier questions I did not had the feeling you understand the difference between power and energy.

Online bdunham7

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The word rate should be self explanatory not sure if I can define that better for you but it has nothing to do with time.

It isn't a good sign when you can't define the terms that you use. 

per Merriam-Webster

Definition of rate (Entry 1 of 3)
1a: a quantity, amount, or degree of something measured per unit of something else


You said 'power is just the rate.....'

So, power is energy measured per unit of......??

Some of the things you come up with are weird and non-standard, but not necessarily wrong.  Like this example I suppose.  Others are just plain wrong.  But in all cases your reasoning is murky and occasionally incoherent.  I  understand power, energy, Newtons laws and all the rest quite well, thanks.  I'm going to finally give up on you.
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Offline msuffidy

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No really, I am not sure what is going on here,but in general, this shape somehow slows down other air around the craft and thus converts this energy into a greater speed for the craft. So conservation is retained as the other air is slowed down. This could have to do with a strong negative energy source against the positive one, caused by the positive one.
 

Offline electrodacus

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So, power is energy measured per unit of......??


It is if I was to define force as impulse per unit of time. Is this making sense to you ?
Force has nothing to do with time same as power has nothing to do with time.


Power is the rate at which work is performed. Energy is the ability to do work and not power.
I will never define power as something related to energy just the other way around where Energy is power times time.
So energy contains time while power is not since is just the rate at witch work is done.


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