[Paraview] Computing a normal derivative of velocity

[Martin Vymazal]

Hello Adriano,

  thanks a lot for your advice. It worked perfect.

  Best regards,

    Martin Vymazal


Quoting Adriano Gagliardi <agagliardi at ara.co.uk>:

>
> 'Generate Surface Normals' requires a vtkPolyData as input. Run 'Extract
> Surface' which will give you a vtkPolyData, which you can generate surface
> normals from.
>
> Running GradientOfUnstructuredDataSet on a scalar will give you a vector.
> You may have to compute the velocity magnitude first and store it as a
> variable before trying to compute the gradient. You can do this using the
> calculator with a function 'mag(v)' naming it something creative like say
> 'mag_v', then selecting mag_v as your input to the gradient computor.
>
> Similarly, to compute the dot product of two vectors, in the calculator it
> is simply '(Normals).(grad_mag_v)'.
>
> ===================================
>
> Adriano Gagliardi MEng PhD
> Business Sector Leader
> Computational Aerodynamics
> Aircraft Research Association Ltd.
> Manton Lane
> Bedford
>
> Tel: 01234 32 4644
> E-mail: agagliardi at ara.co.uk
> Url: www.ara.co.uk
> -----Original Message-----
> From: paraview-bounces at paraview.org [mailto:paraview-bounces at paraview.org]
> On Behalf Of Martin Vymazal
> Sent: 31 August 2010 19:18
> To: paraview at paraview.org
> Subject: [Paraview] Computing a normal derivative of velocity
>
> Dear ParaView users and developers,
>
>   I have an output file of a Finite Element code, which contains a fluid
> velocity vector field. I would like to plot the values of dv/dn on the walls
> of my domain. My idea was this: plot a gradient of velocity magnitude,
> generate surface normals and then compute the scalar product (grad(v),n).
> Unfortunately, I have several problems:
> when I plot the gradient of velocity
> (Filters->GradientOfUnstructuredDataSet), I have a scalar field of gradient
> magnitude (I guess), but no vector field, even though mathematically
> speaking, grad(scalar) results in a vector. Could you tell me how to
> generate a vector field where the vector components are
> (grad(v)_x,grad(v)_y,grad(v)_z) ?
>
> Second, I don't understand why Filters->Generate Surface Normals is disabled
> when I load my data file (in Ensight format). The only way of plotting some
> normals is using 'glyphs', but these glyphs are then not available in the
> 'Calculator' filter which I wanted to use to compute the final scalar
> product (grad(v),n). One strange thing I also noticed is that the glyphs are
> not plotted on a part of the domain boundary (which is smooth).
>
> Could you please give me a hint how to obtain the plot of dv/dn ?
>
> Thank you.
>
>   Martin Vymazal
>
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