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- When creating direction changes in these lines consider the resultant drag caused by the abrupt change in the fluid's path as well as the turbulence it can create, which further affects the pressure and velocity values of the flowing fluid
- The red pockets on the corners symbolize points of flow separation, which just means that the smooth stream is broken up into sections, causing turbulent flow and pressure losses.
- All in all this just means that you should for as straight and consistent as a path as possible, and if you have to, utilize more gradual, smoother turns, as more abrupt and constant turning hurts fluid flow, leads to excess drag, as well as lots of pressure drops and turbulence
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Topology Optimization
Above is a brake pedal mock up I created (bare with me, I know the initial design isn't pretty but it is to showcase how topology optimization can drastically change and improve a design).
- For starters, Topology Optimization optimizes the material use for a part, and it can optimize specifically for stiffness-to-weight ratio, minimal mass, etc.
- This is especially useful on parts that are long/larger and inherently have a lot of material, which can lead to small high stress concentrations and the rest of the material being redundant and unneeded
- All in all, if you are really looking to not just meet design requirements for your part, but truly create an optimized and efficient part, Topology Optimization can be a great help
- Disclaimer: This brake pedal is not necessarily a true brake pedal (aka there is no hole to mount to the bearing bar) but for the purpose of just showing you how top-ops work, this should do fine
Now I am going to run through a simple Topology Optimization setup, what my thought process is, and how to interpret the results.
Firstly, topology optimization utilizes FEA (Finite Element Analysis) to take in stress, strain, factor of safety, etc. etc. to understand how the part reacts to the specified load and situation.
For the FEA, you'll need to set up your material, supports, and loads. For the topology optimization, you'll also need to set your optimization goals.
- The material is self explanatory. Just ensure that if you are using lets say 6061 aluminum, are you using 6061-0, 6061-t4, or 6061-t6 aluminum? These just signify the different types processing the metal are put through, which are important to maintaining accurate numerical properties and therefore simulation data
- In terms of loads, this can be as simple (or complicated depending on what the part/situation is) as drawing an FBD and replicating all the forces acting on the part. Also, remember to check your units when simulating, as 1000 N is very different from 1000 kN
- Supports are majorly important, as stated earlier. The topology optimization itself is predicated on the FEA results, so any over or under constraining will worsen your results, especially when you are literally optimizing a part based on faulty results
Consider this wall-mounted hook/bracket design. The bracket will be screwed into the wall via the top hole, with half the bracket resting on the wall, and the other hanging with the force applied.
Look at these different support setups for a wall-mounted bracket and try and get an understanding of how they would affect your simulations and therefore your results.
- With an under constrained setup, only the top screw hole is fixed, meaning that your simulation would have too little restriction and results where the model displaces and translates far higher than it would actually in use. This is because the side that rests on the wall is allowed to bend essentially into where the wall would be. Therefore, this setup results in a poor and inaccurate simulation
- Just to give a definition of under constrained, this means that there are insufficient motion/deformation restrictions and that the number of constraints is fewer than the DOF (degrees of freedom). Degrees of Freedom just refer to the different variables that make up the possible motions of a system (so think of each translation in the X,Y, and Z to be each a single DOF, each moment on each axis being a single DOF each, etc. etc.)
- With an over constrained setup, you'd have the entire back of the bracket essentially bonded to the wall. This is unrealistic because you are basically assuming the part is stuck to the wall no matter the load, which will not happen in a real situation. Therefore, you get a simulation results that poorly represent what will actually happen, showing too little deformation for the situation
- Again, just to give a definition, you have too many motion/deformation restrictions and the number of constraints is higher than the DOF if you have a over constrained setup
- In a well constrained setup, you'd have constrains to mimic both the screw going into the wall and a proper translation constraint to keep the part from bending back into the wall. This gives you a realistic situation, simulation, equilibrium, and results
Now let me show you all this through the situation of the brake pedal.
For this rather elementary part and situation, all I am assuming is that the pedal is bolted only at the bottom (realistically we would have a balance bar mounting point)
Additionally, in this case, we are simulating in the case that the brake is already pushed down and that the driver is now attempting to push the brake pedal past its limit. This is basically a safety check to ensure that in a tense situation, due to adrenaline or whatever other extenuating circumstance, the brake pedal will not break (lol) in a situation where it cannot move anymore past its limit.
- If you were simulating in a case where the brake was at its starting position, you would utilize a hinge support, which would restrict the circular edge of the hole in all 6 DOF except for rotation around its own axis. Basically the brake pedal can only move like it would in real life, rotating around the bolt.
In terms of external loads, we simply have the a 311 N force applied normal to the pedal contact area (this number represents the force of an average person pushing the brakes, about 70 lbf) as well as the gravitational force acting at the center of gravity (as the pedal is being actively pulled down since the top part is essentially floating in air).
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Useful Tidbits
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