Hi, Stephanie--

I do this kind of thing with field_parameters. On some data object, you call

>>> object.set_field_parameter('vzmean',478)

then in your field definition, I do

def _Eturb(field,data):

vzmean = data.get_field_parameter('vzmean')

return data['z-velocity']-vzmean

add_field( 'Eturb', _Eturb, validators=[ValidateParameter('vzmean')])

So in your analysis, you

1.) define some object, as you're doing,

2.) set the field parameters on that object

3.) call your function

and to define the function, you need to

1.) call get_field_parameter to retrieve the value

2.) use the ValidateParameter validator to have yt error check that you have the field defined. (This, I believe, should be a list of ValidateParameter for each vxmean, vymean, and vzmean. Alternatively, you can supply a bulk velocity as a vector, which is my preference.)

I hope that helps. Let me know if you want me to clarify anything.

On Mon, Dec 2, 2013 at 3:49 PM, Stephanie Tonnesen <stonnes@gmail.com> wrote:

Hi yt-users!

So I want to calculate the turbulent energy in a stripped tail of gas. This tail is moving with a bulk flow in the z-direction, which varies as a function of z, and is rotating, and v_theta will also likely change as a function of z (and while I am at it, might as well check v_r). So I would like to do something like this:

def _Eturb(field,data):
    vrmean = value I calculate in the code
    vthetamean = value I calculate in the code
    vzmean = value I calculate in the code
    return(pow(data["cyl_RadialVelocity"]-vrmean,2) + pow(data["cyl_TangentialVelocity"]-vthetamean,2) + pow(data["z-velocity"]-vzmean,2))

add_field("Eturb",function=_Eturb,units="velocityunits")

totalEturb = np.zeros(100,float)
pf = load("id0/rps."+outstring[i]+"
.vtk",parameters={"TimeUnits":9.78262,"LengthUnits":26.,"DensityUnits":9.999e-30,"VelocityUnits":2.6e8})

alld = pf.h.all_data()
i = 0
while i < 100:
    disk = pf.h.disk([0.0,0.0,i*0.385/2.],[0.0,0.0,1.0],1.0,0.385)
    vrmean = disk.quantities["WeightedAverageQuantity"]("cyl_RadialVelocity","Ones")

    vthetamean = disk.quantities["WeightedAverageQuantity"]("cyl_TangentialVelocity","Ones")
    vzmean = disk.quantities["WeightedAverageQuantity"]("z-velocity","Ones")

    totalEturb[i] = disk.quantities["TotalQuantity"]["Eturb"]
    i = i+1

I am not sure if/how I can make the def statement read in vrmean, vthetamean, and vzmean?

Thanks!

Stephanie

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