Parametric spline modification (rotation/translation)

[giulianoj.zennaro]

Hello,

After multiple searches on the forum, it appears to me that there is no way to parametrically edit a spline. The scale tool is the only one that is usable, whereas there is no way to move the spline in a rigid manner. Constraining one of the points of the spline to something which is parametrically defined in space also does not work as the spline is not updated properly when the parameter is changed. 

This issue seems to affect few people, however it has been the case for years with already several people mentioning it and no viable workaround. Here is an example of a post clearly describing the issue with images : https://forums.autodesk.com/t5/fusion-design-validate-document/how-to-fix-the-relative-shape-of-a-sp...

In my specific case, I need to design a wing parametrically since I want to export multiple step files with slight geometric variations for CFD simulations. One of the parameters I need to modify is twist and so the profile (spline) at one end of the wing has to be rotated parametrically. Another parameter I have involves the translation of a profile. Obviously, being an airfoil, the splines are made from far too many points to manually constrain them all (I use airfoil DAT to spline).

Have there been any updates on this necessary feature, new viable workarounds or a separate possible workflow for my specific use case ? 

Thank you in advance for your time and suggestions !

PS : for the twist variation, I have a possible workflow which I still haven’t tested. I could draw one profile at each end of the wing and multiple construction lines representing the chord along the wingspan. The construction lines can easily have their angle changed from parameters and I can connect them all in 3D with lines or splines which then can be used as rails for a loft. For the second profile, I can then manually rotate it each time, export the model and then rotate back to zero before choosing the new desired twist. My issue here however is I’m not sure I can select a curve which is composed of multiple splines or other curves, even if they’re coincident and tangent (another major issue I have run into), as a rail.

[Drewpan]

Hi,

I may not be able to help you with your specific fusion problems but I may be able to help with twisting airfoils.

When I was creating this wing I used one of the free plug ins from the App store for airfoils. It used a standard

airfoil data like dat or another. I cannot remember. One of the features of the App was to enter an angle so that

twist was automagically created in the airfoil spline when you created it.

These are the three airfoil Apps I have installed right now, it was one of them but I think the middle one.

The end result I got was a compound wing with two airfoils blended together with loft and a 2 degree twist.

Cheers

Andrew

[davebYYPCU]

Did you read that thread, or just the first question.

Why are the solutions in that thread not an option?  (Component / Joint)

Are you twisting the LE, TE or other?

Multipaned wings?

Airfoil Libraries?

PS I have no idea about outputting to CFD stuff.

Might help....

[wersy]

What you have in mind cannot be realized with Fusion and is not intended.
For fully parameterized wings there are special programs such as Wing Helper.

https://www.winghelper.com/default/index.php/de/

[davebYYPCU]

What you have in mind cannot be realized with Fusion and is not intended.

Bold statement.

[giulianoj.zennaro]

Thank you for all your answers.

Making the wing is not an issue @Drewpan, the issue is having it update automatically. I have tested several add-ins and although I can put a user defined parameter when creating the airfoil, if I then change that parameter, the geometry does  not update.

Same issue with moving an extruded spline as proposed in the other post @davebYYPCU. I can indeed move it once with a parameter, however that move command will not update with later parameter changes. 

@wersy, indeed a bold statement, but I fear you seem to be correct. It seems a pity since most of the infrastructure needed is already in fusion, so why not add that capability ? All that would be needed is a fix sketch command that does not constrain the 2d position but leaves that free to be constrained by construction lines. Is there any way to propose such a feature ? In the mean time I'll have a look at wing helper and keep thinking about workarounds that are realistically usable (time-wise) in  fusion...

[giulianoj.zennaro]

What I am trying to model is an AC72 wing sail (a rigid wing used as a sail on a sailboat). The twist requirement comes from the wind itself being twisted and because of the need to de-power the sail in rough conditions. In real life, this is achieved by having multiple flaps independently actuated. Since I want to simulate this, I would rather have a smooth continuous twist to avoid having small faces and gaps which are a numerical nightmare. As you can see here, the rotation point is at the back of the front wing element (no twist in this image, just camber. The twist would be like camber that increases with height).

 The problem I have is modelling the winglet (not there in real life). If I want to be able to easily modify it, the two profiles I use have to not only scale parametrically, but also move.

As briefly mentioned I also have another major issue concerning the winglet. I assume that the shape would be smoother if I did one loft passing by the two profiles rather than two separate ones. First of all, is that true ? If so, my issue is selecting the guide rail as it is made from a straight line and an arc.  Although the combination of the two curves is coincident, tangent and touches both profiles I cannot select it as a rail since I cannot select the two curves in one go.

And finally, yet another issue, for some reason, if I use rails to model the winglet, the mirror tool no longer works.

Seems like a lot of "nearly achieved" features which is a pity... Unless I am doing something wrong.

[davebYYPCU]

Attach the example file, with a list of parameter changes desired.

Whilst Fusion has some limits, I believe what you want can be done.  

You want to move and position a tip airfoil, with scaled parametric changes to airfoil / washout, can be done.

Might help….

[MichaelT_123]

Hi Mr Giulianoj.Zennaro

“In my specific case, I need to design a wing parametrically since I want to export multiple step files with slight geometric variations for CFD simulations.”

It is a formidable task … particularly if you plan to approach it … by manual labour of constraining splines/sketches. As you talk about ‘wing simulation’ in CFD, you should realize that the surface quality must be meticulous for high Raynolds numbers (as in the case of a wing’s airflow). It would be practically impossible to achieve such an outcome across multiple generations of a design … using a manual drawing strategy. The quality of CFD software and the capacity of the hardware are also important here … if you want to achieve reliable study objectives. CFD simulation of an aircraft wing differs from CFD study of, e.g. a computer enclosure or smoke in a chimney… not only by the complexity of the respective algorithms but also … by the size of a hole in a pocket for necessary software/hardware infrastructure … even before taking on the results verification step hurdle.

Well, of course, the types of objectives you have are essential factors here. You know them better than everybody else.

For severe work … automation is paramount here … “fondling a mouse” is not necessarily the option leading to reliable results.

On a side note, for your information/entertainment, I will separately post visuals of a propeller model as an example of 'twisting things’ (which belongs on the Forum to the same family as ‘spiral things’†). The model is controlled not by simple scalar parameters but by functions.

All the best with your project!

† https://forums.autodesk.com/t5/fusion-design-validate-document/hose-with-a-helical-wire/m-p/12870727

Regards

MichaelT

[giulianoj.zennaro]

Here is the file with the trailing component (the image above was another file where I simply assembled the components together).

As you will see in this file, I made several profiles along the wingspan. I assume I could have limited that to only the two extremities and instead use rails and construction lines in between.

You will also see what I mean by the mirror tool not working and the rail problem (in this case I just made two lofts). I basically want to mirror the winglet for it to be symmetrical.

[davebYYPCU]

I did not see message 7 at time of writing message 8.  I stand by my offer.

Mirror command requires New Body setting when there is overlap like you are doing.

So you are only worried by the winglet/s?

Might help…..

[giulianoj.zennaro]

New body indeed works thank you !

What I would need would be to be able to parametrically rotate the naca 0012 profiles along the wing span to obtain a twisted wing. Furthermore, if you look at the parameter list, I would like to be able to change the dimensions of the winglet (height, semi span, chord ratio). That involves scaling the naca 0006 profiles and offsetting them. (the initial scaling and offsetting which was inputed with a parameter does not update unfortunately when I change one of the values)

[wersy]

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@davebYYPCU  schrieb:

What you have in mind cannot be realized with Fusion and is not intended.

Bold statement.

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You don't have to be bold to say that 🙂
If you've been designing wings for 12 years, you know what you're talking about. It would be going too far to list everything that a fully parameric wing contains.
I am delighted if I work on a wing for a few weeks without my “client” asking for a change. Since I know all the problems, I really clarify all the details in advance and make suggestions.
To be honest, with Winghelper it would be done in a few days.

[giulianoj.zennaro]

I have to admit I still don't know the feasibility of such simulations. I would like to do this as part of a CFD course I am taking at university using Ansys. I am not sure yet what license we will have access to.

In therms of the surface quality, why would changing the span for example or the twist be an issue ? I was aiming to export several step files and mesh them each independently for independent studies.

[wersy]

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@MichaelT_123  schrieb:

you should realize that the surface quality must be meticulous for high Raynolds numbers (as in the case of a wing’s airflow).

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High Reynolds Numbers?

I assume that it is about models, i.e. Low Renolds Numbers.
There are programs such as XFLR5 for this.

http://www.xflr5.tech/xflr5.htm

[TrippyLighting]

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@davebYYPCU wrote:

What you have in mind cannot be realized with Fusion and is not intended.

Bold statement.

---

But completely true!

@MichaelT_123 shows how it can be done in Fusion, but his solution requires in-depth knowledge of the Fusion Python API, significant programming experience, and last, but by no means least, in-depth knowledge and experience of the underlying math and  algorithms.

[davebYYPCU]

I have reviewed the file.   Somewhere you asked or am I doing something wrong?  Yes Sir.

I am yet to understand the description of the parameter changes you mention,

but I will work that out, eventually.

Lofting from rib to rib will not give you smooth flow, just straight segments. 

Each rib must have taken a lot of time, and the whole thing is not best workflow for Fusion.

Are you happy with this Lofting thickness result? (Loft 13)

So the main panel Leading edge is straight.

The Trailing edge of the Winglet is parallel to main panel LE, 

Transition from Naca 12 to Naca 6 is around that bend?

Am I correct - you wish to change

Winglet tip rib Chord Length,

Winglet tip rib height (semi span) and

maybe washout angle?

[MichaelT_123]

Hi Mr Wersy,

Reynolds function vs velocity and fluid viscosity is highly nonlinear, approaching significant values for a high ratio of the two. Its mean/maximum value ranges are the main difference between algorithms simulating smoke in a chimney, slow plane, ... vs, e.g. turboprop, F35 wing...

The respective differential equation becomes... stiff ..., and the underlying matrices become hard to solve.

Reynolds numbers are also non-uniform along moving surfaces and, even at slow velocities, become very high at the edges or protrusions ... generating turbulences. Still, nobody knows who was the first Reynolds number or turbulence, but everyone agrees that they contribute significantly to drag coefficients of moving through viscous medium objects.

Regards

MichaelT

[davebYYPCU]

Fusion can make this model, using the right tools for the job.

Step up the timeline, happy to answer questions

Might help.....

[MichaelT_123]

You are too kind Mr TrippyLighting.

Regards

MichaelT