Flight dynamics analysis
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mjennings
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Likely will depend on which modules of Ansys you have access too. If you just have the the stress analysis tools you can likely do some approximations at loads and get reasonable answers. If you also have the full cfd tool kit (If it exists, I know several years ago many of the analysis software packages were working on multi mode solvers, but I haven't kept up with it) you can do a full flight sim. But this is no trivial task if you are new to FEM/CFD modeling most software packages have a big learning curve.
Hi, thanks for the insight.
Actually as part of the final year undergraduate project, our team is given the flight dynamics analysis. Another team is there for design, and another team is for motor (solid propellant).
A lot of info is available for other teams, but since our team has cfd simulation, knowledge is very limited for us. ( my elective subject is introduction to CFD, and i have pretty good command in fluid mechanics, solid mechanics and mathematics)
But i am new to CFD simulations using packages like ansys. Only have theoretical knowledge which was gained through elective course, which didn't had any lab classes)
I tried to contact a company which gives training on CFD projects, and they told that Ignoring the dynamic mesh method for vehicle fluctuation, applying a steady-state solver it cost around 310dollars.
also if Dynamic derivative meshing is needed for finding pitch, yaw etc it will cost around 650 dollars.
So, which option is better, since we wish to do the project as good as possible.
I think a full flight simulation is beyond the scope of an undergraduate course, or is it feasible?
mjennings
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Yeah full flight dynamics is likely beyond your time/budget/class scope. I had a graduate level CFD and all we did was 2d heat transfer. That is a very interesting way to set up design class teams, since everyone is dependent on the design team. Assuming your design has fins, start with Barrowman equation to check low AoA stab assumptions. A lot of aircraft stab and control equations are similar to rockets if you have a control system. Check some S&C books for equations. Open rocket/rocsim have some analysis tools. Talk to your professor understand what they are looking for and if they are willing to give you guidance. I used Roshkam's and Raymer's design books in senior design I can't remember if they had rocket sections. Since a rocket is mostly radial symmetrical you can do a side view 2d CFD with the rocket and fin profile. Also you could build flying models and have video of flight test in your presentation.
Hi, thanks for you valuable insights
When I retired 13 years ago Fluent was the CFD computer code that we were using. Among other things Fluent was based on finite differences. I remember Ansys, which uses finite elements, was the computer code used by the structural engineers. I remember that there was an engineer in our Fluid Dynamics group that said CFD based on finite elements was the coming thing. I remember that finite elements and Ansys for CFD never came close to catching on in our group.
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Yes, finite volume method is used for solving fluid flow and heat transfer problems.
Finite element is used for structural analysis.
Finite difference I think has become obsolete.
OK, I just checked with Google and it seems that Fluent and others have gone with finite volume. Interesting. Times have changed. (Or maybe Fluent was finite volume and I forgot.) I do remember before I retired, I had a difficult 3D problem with about 6 million cells, which had a hard time starting the calculation, bombing after only a few iterations. I found that for myself I had better results when using cells made of bricks rather than using the automated unstructured pyramid cells. From Google it sounds like perhaps that unstructured cells have caught on and are stable. I know setting up unstructured cells automatically is a lot faster than trying to set up cells as bricks by the individual user.
Note that Finite Volume and Finite Element, although both are numerical methods, are not the same thing.
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Finite element analysis is a way to make a model into a lot of simultaneous equations then solve the unknowns. You break a model up into elements then write equations about the stresses/forces at the edges of the elements with respect to deflections/movements. Then you assemble all of the elements together and that creates a big stiffness matrix (simultaneous equations). Now solve for the displacements. Consider if you have a building and you let wind push on it- the roof moves sideways, the ends of each beam and column have different movements including sideways movement and rotations as the pieces bend. These are unknowns that you solve the simultaneous equations to get. I got interested in finite element analysis in college and wrote a number of analysis programs in Fortran to run on the school's mainframe. Later when personal computers became available I ported the programs to those, a lot of buildings have been analyzed and designed using my programs.
Finite difference in structural analysis is a way to solve a differential equation of bending by using a series approximation. The boundary conditions have to set to certain conditions to make the series work out. It was a way to solve problems with low computational power. It isn't very flexible, hard to apply to certain types of problems. Once more computer power was available finite element analysis took over, although there are some specialized areas that still use finite differences I assume based on the principle of "if it's not broke don't fix it". I never liked this type of analysis because the boundary condition restraints were too restraining.
