Spring simulation

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1. Jul 8, 2017

mech-eng

How can I simulate this spring system and see how they move and behave?

Thank you.

2. Jul 8, 2017

Staff: Mentor

Looks like it's for schoolwork...

What simulation software do you have access to? Heck, you could even just simulate it in Excel and generate plots in Excel...

3. Jul 8, 2017

mech-eng

I can access to ansys, autocad, solidworks and some others may be comsol but the difficult part is that I am not good at using them.This is why I ask here the questions. We can divide the topic into softwares but I need the steps. I hope someone give the steps for these common softwares or a link showing what I want to do.

I haven't known excel can be used engineering simulations. I can have access it to as well.

Thank you.

4. Jul 8, 2017

Staff: Mentor

So it is for schoolwork, but sometimes simulation threads are allowed in the technical forums. We'll see how this goes, but you need to show LOTS of effort when posting advanced schoolwork in a technical forum.

What are you simulating? Are you supposed to simulate the extensions of the springs based on different attached masses? Are you supposed to calculate some oscillations?

Try starting with Excel and just write the equations for the extensions of the springs as a function of the weights.

5. Jul 8, 2017

mech-eng

No, it is neither for schoolworks nor there is an obligation for it, it is an arbitrary work. So why do I want to do it. Just for learning. Just for to go one more step ahead. I would like to show these efforts.

I want to simulate that mass-spring system, a crane. No I would like to simuate springs with angles. I cannot imagine and understand how they will move, I cannot understand how their motion is.

I do not know how I can write those equations. I know just F=kx for springs.

Thank you.

6. Jul 8, 2017

Staff: Mentor

Well, the right-hand one (c) is easy, right? You write F=kx, displace the weight slightly from the equilibrium position, and write the equation of motion for the weight. Then in Excel you set up two columns, with the first column being time steps (say 1/100 of a second, or 1/10 of a second) starting at 0, and in the 2nd column you paste in the equation for the motion as a function of time. Then you can plot a graph of the motion of the weight as it oscillates vertically.

Then one step further is to write the equation for the displacement of the weight in one time step given the current position and the forces on it. The force is F=kx where x is the displacement. So then in Excel, the first column would be time, the 2nd column would be current position, and the 3rd column is the new position over that time step given the initial position and the force on the weight to cause it to move.

Maybe give that a try to get a feel for simple simulations. Using the simulation software packages like ANSYS hides some of this from you, but it's good to have a feel for what the FEM simulation software package is doing...

7. Jul 9, 2017

JBA

An undamped spring and weight combination (the right side example) will always oscillate at it s natural frequency. Look up the equation for that category of vibration and you will get the appropriate equation for your time function simulation calculation.

8. Jul 13, 2017

mech-eng

Yes, it is the easy one. Left side example is harder one to which I am more interested in.

Thank you.

9. Jul 13, 2017

JBA

I think your statement on the increased degree of difficulty is an understatement.
I did a little time reviewing my old university vibrations course textbook and the best I can offer from that is that the spring combination regardless of the linkage configuration is treated as a simple parallel spring case resulting in a single equivalent spring rate.

At this point, I am going off of the track a bit by offering you a bit of my speculation on how you might proceed from there. Your geometry that results in unequal spring displacements and clearly that considerably complicates the situation; but, an equation determining the displacement and the force at a given displacement of one spring to other spring based upon your linkage geometry is rather straightforward. It is then necessary to write an equation relating the motion of the mass to to one of the springs and by combining that with the first equation you should have a single equation relating the mass motion to the spring linkage system response.

Unfortunately that is about as far as I can get you. In order to utilize this to a determine cycle frequency you might start by researching the simpler case of a single mass oscillating longitudinally between two springs and seeing how that might be tied to your prior consolidated system equation.
I hope all of this might help give some help.

Last edited by a moderator: Jul 13, 2017
10. Jul 13, 2017

Nidum

This problem with two springs is more or less difficult depending on how the motion of the mass is constrained .

If it is constrained to just move up and down then solution only requires resolution of forces and displacements into components along the springs and along the vertical axis . Otherwise it is essentially the same as the one spring problem .

If it is completely unconstrained then the motion of the springs is going to be two dimensional . This may result in a motion in a straight line at an odd angle or in an elliptic type motion . Not impossible to solve but certainly not easy .

Note that a real world version of that mechanism would wobble all over the place or just fall over in the front to back direction . You have to assume for the purpose of answering this problem the fictions that all motion takes place in the 2D plane containing the spring axes (ie the plane of the paper as drawn) and that the springs deflect true along their own axes and don't have secondary lateral deflections or buckle completely .

Last edited: Jul 14, 2017