Hi all,
I am a graduate engineer learning FEA, I am doing a simulation on a Pump and Engine Skid frame, I would like your professional input if possible. I have different Ideas on how to apply the loads and boundary conditions, wanted to know if i am on the right path. i am using Prepomax and model was prepared in solidworks. specs are listed below.
Engine Specs:
- power: 297kW
- mass: 1285kg
- RPM: 1800RPM
-Torque: 1560 N.m
Pump Specs:
-mass: 1400 kg
Loads used in FEA simulation
pump weight with 1.5x safety factor = 20.6kN
Engine weight with 1.5x safety factor = 18.91kN
Torque with 2.5x Safety factor = 3900N.m
I assigned 2 reference points at the height of the input shaft on the center for both the pump and the engine. the reference points have a rigid body constraint to the pump base (green) and engine mounts (orange). the skid frame sits on 6 antivibration mounts (marked in black) I have used those as the fixed point. lastly, the torque was applied as a moment to the reference points (purple arrows, opposite directions for pump and engine). the last photo shows the results. how accurate are they? how should i go about doing the hand calculations to verify the results?
other ideas i had for the boundary conditions:
- creating reference points at the center of each mounting hole of the frame and setting those as the fixed locations
- applying the weight of the pump and engine directly to the base instead of the reference point (will this be more accurate?)
-adding another reference point for the both the engine and pump at their COG to apply the weight force from there
Thank you all in advance
Anti-vibration mounts are likely very compliant so it might be better to model them as point springs (you would need to know their stiffnesses though) attached via rigid body constraints.
You would have to simplify this setup significantly to use hand calcs (e.g. split it to individual beams or subframes) but those are not always necessary. There are other ways to verify the results - check the reaction forces, stress concentrations and so on.
PrePoMax supports both point and distributed mass: https://www.youtube.com/watch?v=DruuOWn3PKs
The latter can be useful when you don’t want to make a surface rigid (since that’s what rigid body constraint does). Just remember to define a separate gravity load for mass section, as shown in the video.
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Hi, I make also skid desing/fea. Normally I mesh with second order hexa elements using at least two elements in thikness, meshing with only one tet element in thikness sometimes is not very accurated. BC looks ok, I would add some extra worse load case, with the skid supported only by four points in the ends (even if you specify six or eight mounts for normal operation, very often for lifting and storage they remove the soft mounts and use hard supports only in the ends). You must analyze also the lifting operations, will they use only four points at the ends? If your deformation at the middle is too high and the lifting is done with the coupling mounted, it can damage it.
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thank you so much for your feedback i really appreciate it
thank you sergio for the feedback and recommendations. in order to increase the number of elements in the thicknesses do i use mesh refinement and select the thickness regions?
also a question in regard to the rectangular cut outs in the C channel, in your experience, is there any considerations to be taken in to account for the design of them and supporting the structure around the cutouts?
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You should work with at least two elements in all members, if you want to make it with tet elements, then the quantity will be so huge that cannot be possible to solve due to memory limitation. The only way to get these two elements, is meshing with hexas and controlling very carefull the quantiy of elements, not only in thicknes but also along the profiles to get a manageable mesh. Is a complex task to get an hexa mesh, these lasts versions of PrePoMax brings several options to make it (extrude, sweep…) and refine it, but again, takes time.
I´m preparing some examples to make an specific training in meshing (including hexas) using open source tools, based in PrePoMax and other available tools.
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amazing, the mesh you generated is very impressive. looking forward to your instructional videos Sergio. is there any books or recourses that you recommend for Skid design? so i can increase my knowledge?
