speed test and aerodynamics

[cees10]

Hello evry one

I  have a problem and have no idea how to solve this in didam , i must develop a measuring device for determine the aerodynamic property of a object

I have some sample data   as  attached

it a speed in 0.1 of a second let say the object is 120 kg

know the problem comes to define the calc  of the sample data , i really have no idea how to do this in didam hope some can help me out

i want the   I mol   and    aerodynamic number     also the  must be automaticly   see where ths speed is max   and the do the calc if the speed drops to a speed where the curve can still fiitted 

any one a idea?

i would be gratefull

After this i could make the real hardware  ,where is it easy to find the values

Cees

[Brad_Turpin]

Hi cees10,

I have loaded your attached data into DIAdem.  You appear to have a data set that is acquired at 0.1 second intervals and runs for almost 32 minutes and contains about 6 main (2 stage) cycles, with a lot of scattered outlier points.  The cycles appear to come in two groups of 3, with a bit more time separating the first 3 from the last 3 than between each of the rest of them.

Your data set has no channel names and no channel units-- just data points in two columns. What should I make of your 120 kg reference?

Your question appears to be contained in the partial sentence, "...know the problem comes to define the calc  of the sample data...", yet I can not make out what you are in fact asking.  You also state, "...i want the   I mol   and    aerodynamic number...", but this does not make anything clearer.  By "mol" do you mean a mole of atoms, as in Avogadro's number "mol", or do you mean something else?  What is the "aerodynamic number"?

I can certainly help you identify where the speed is maximum, assuming the first column in your data set is the "speed" column, but this will be more difficult because of all the noise.

Please try to restate your questions more carefully and clearly.  In case it helps, I'm attaching a TDM/TDX file of your data set, which will load directly into DIAdem for easy plotting, and I'm also attaching a VIEW layout *.TDV file that plots your data with markers to more clearly distinguish between data and all the noise you have.

Brad Turpin

DIAdem Product Support Engineer
National Instruments

[cees10]

Thanks Brad

Well becuase i am not a american i problem to find the right words

But first i am seeking to the moment of inertia      

And the aerodynamic coeff  , roll  coeff

As we know the mass   120 kg   

the test is a coast down of a vehicle    i want to extact the values for this coast down test

the speed is in the first collom    in km/h             wich is indeed 0.1 sec to have a good output for the  test    the second one is  the time 

as you already have find out i have 2 pair of 3             to    test  2 differant vehicle's

hope to have things more clear .

Cees 

[Brad_Turpin]

Hi cees,

I now understand that you are seeking the moment of inertia, the aerodynamic coefficient and roll coefficient of a 120 kg vehicle that is undergoing a coast down test.  I think you said that this test data set you sent contains two such tests, perhaps on two different vehicles.  I also now know for sure that the first column is speed in km/h and the second column is the elapsed time of each 0.1 sec measurement.

Unfortunately, I have no idea how to calculate the the moment of inertia, the aerodynamic coefficient or the roll coefficient from a time and speed series, even knowing the mass of the object.  It doesn't seem to me that we have enough information to distinguish between these quantities based purely on the coast down speed profile.

Also, there's the complicating factor of all those noisy measured points.  How do you plan on differentiating between real data and noise in this data set?  Perhaps if you only look at one part of each two part cycle you can avoid the noise.  Why are there 2 parts to each coast down measurement-- the tall peak and the flat peak?

Finally, what is your native language?  If it's German or French, perhaps we could make more progress in your language than mine?

I'm including a DataPlugin you can use to load your data sets into DIAdem.  First, detach the *.URI file and double-click on it in Windows Explorer.  Then if you start with data in Excel, just export the Excel worksheet to a tab-delimited *.txt file, then drag the resulting *.txt file from the DIAdem NAVIGATOR into the Data Portal.

Brad Turpin

DIAdem Product Support Engineer

National Instruments

[cees10]

well thanks   Brad

my  speech is dutch

and this is the formula for distract the values i need inside the jpg

meaby this helps to solve the problem

cees, 

[Brad_Turpin]

Hi cees,

Well, I'm not good at reading Dutch, how's your German?  I'm fluent in German.  Your formula looks very nice, but you didn't define any of the variables in it.

Normally the omega ("w") variable means angular velocity.  You said that the speed channel in your data set was linear speed in km/h.  So.... how do we get the omega ("w") value from your data?

Your equation defines a variable t(w), what does this "t" variable mean?  Is it time, or something else?

Your equation has parameters "a", "b", "c", what values do we use for these parameters in your equation?

I also believe you said earlier that you wanted to find the maximum speed for each cycle-- how would that figure into this equation?  Also, would the equation apply to each of you 6 cycles separately?  If so, how do we define the starting and ending X values for each cycle?

Brad Turpin
DIAdem Product Support Engineer
National Instruments

[cees10]

HI brad sorry for the delay but i was so busy

T= time

W=work

t*w = power

a=force

b=force

C= aerodynamic property's (so basicly the total force of air to that body coeff)

In the equation there is nothing to find the max speed

i want to apply the formula on all 6 cycles separate (when it goes from top down to a certain speed,in wich i must give a manual numer)

[Brad_Turpin]

Hi cees,

Thank you for defining those variables-- that helps.  Unfortunately, none of that information is in the data file you posted-- it only has time and speed values.  How should a DIAdem VBScript know what the constants or variables in that formula are?  Can any of them be calculated from time and speed?

Brad Turpin

DIAdem Product Support Engineer
National Instruments

[voogt]

Well you can

Becuase we have the weight (mass)  and the speed and time we can calc the rest   also the friction (roll coeff of the tyre's) in wich its assumed linear we can calc

because we have also the speed and becuase the reduction of te speed you get a curve   from the curve  we can extract the roll coeff

Mass is 120 kg 

[Brad_Turpin]

Hi vogt / cees,

Great, I'm an expert in DIAdem, and you guys are experts in aerodynamics.  Between us we ought to be able to get this to work.  I can help you remove all the noise from your data, find the maximum value of the whole data set as well as the maximum of each cycle, and finally run an equation over each of the 6 cycles separately.  You need to help me understand what the equation is and how to get all the inputs to the equation.  I now have the equation:

t*w = (2*arctan(b+2*c*w/(sqrt(4*a*c-b^2))))/(sqrt(4*a*c-b^2))

and I know that the "t" value in the above equation is "Time", which is 1 of the 2 data channels in your data file.  But "t*w" is the result of the formula, not one of the inputs.  Does that make this formula a curve fitting equation?  Either way, I need to understand how to get the rest of the inputs from the 2 data channels plus additional information we know to be the case, such as "mass = 120kg".  So, let's look at the equation inputs:

w= work
t*w = power

a= force
b= force
c= aerodynamic property's (so basicly the total force of air to that body coeff)

I still have no idea what values to use for "a", b", and "c", and it appears from your description that "a=b", which I doubt is true.  If I could calculate "work" from the Time and Speed data channels, then I could easily get the "power" channel.  Should I differentiate the Speed channel to get an Acceleration channel, which I assume is due to the friction you speak of?  In that case I could multiply the Acceleration channel by the mass to get the Force, and multiply the Force by the Displacement to get the Work.  I could get Displacement channel by integrating the Speed channel

F= ma = (coeff)N = (coeff)mg

W = F(x-x0)

Where (coeff) is the friction coefficient, often denoted by the Greek letter "mu", and (x-x0) is the Displacement.  Please let me know if you were assuming all this to get the "w" variable in the equation or let me know if there is a different process to get "w".  This would take care of "w" and "t*w", but what should I do with the rest of the equation?  fit the Power channel with this equation?  Do we know the value of "a", "b", or "c", or would this be a 3 variable non-linear curve fit?

Brad Turpin

DIAdem Product Support Engineer
Nationa Instruments