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I think I am good now...thanks for all of your help. The reason I was so hung up on the angular acceleration was you need this to figure out the load on the gear teeth. Using the equation "t=V/a=V*I/(T-Tf)" solved this problem as I can compute how fast things really do get up to speed. Thanks...

I should back up a couple steps. The minimum time to get up to speed is not a requirement...the motor just has to have enough power to rotate the drum. Now being that the motor interfaces with a 50" bearing with a 42" internal gear I am trying to do 2 things: 1. Verify the motor has enough...

The motor is actually driving a bearing with an internal gear so the ratio is not exactly 19000:1. In any case what I did was solve for the torque inertia assuming some angular acceleration based on some delta t. Then I compared the resulting torque (including bearing friction) to the torque a...

Thanks zekeman. Dumb question but if I choose a motor with a higher torque does this simply mean the acceleration time will decrease? The is the issue I am running into is this motor is driving an internal gear and I am checking the loads on the teeth.

So I updated the design such that a motor/gear box drives an internal ring gear. I ran through the calcuations again and say if I set the acceleration time to be 1 second the required torque is less than the output torque of my existing motor/gear box combo. Does this mean I need to vary the...

Thanks for all the responses. Just to clarify I haven't caclcuated the HP yet...just know that I can get there once I figure out the torque :) I guess the thing I have a hard time getting my head around is no matter how large the inertia the angular acceleration will always be a positive value...

So I am working a design to rotate a large drum at 5 deg/min (very large inertia) sitting upright on a bearing. I am able to take care of the gear ratios and motor HP calcs but what I am stuck on is how to determine the required torque to move this drum. I know that T = I*alpha but I can input...

abusementpark, I am basically modeling an accelerating beam under a 1g lateral load. eelco, Yep, I quickly found that out and have been able to get the NASTRAN results to match theory but performing a nonlinear analysis w/ large deflections enabled.

The model has about 500 time step so I went for plan b. Apparently the nonlinear dynamic solver doesn't know how to handle CELAS2 elements (but the nonlinear static solver does...) Back to the drawing (or modeling) board!

Ok...one more question. Now that I have the static nonlinear case to work, I am trying to perform a nonlinear time history simulation. I assumed this could be done with the nonlinear dynamic response solver but I don't get any ouput. Is there a trick to get this to work?

Got it, getting the results I am expecting. Thanks a lot rb1957.

The mud is actually turning into murkey water now! We do have the non-linear static and transient solvers in NASTRAN, so if I understand you correctly this non-linear solver will take into account this extra bending due to the axial load in the CBEAMs?

Well that being the case, would it be correct to determine the deflection of the beam due to lateral loading first, then determine the additional bending loads to the axial load acting offset from the undeformed beam centerline? According to Roark, deflections due to axial and lateral loads...

Thanks Ed.R. Dumb question but is this a 'flag' in NASTRAN where I can enable this option?

Not really. If you have both axial and lateral loading, then the deflections/moments will be greater than if you have lateral loading only (assuming the axial load is in compression...according to Roark, Table 10, case 2a for example).

It appears that NASTRAN can not compute bending due to an axial load...is this true? For instance, I calculated the deflection of a beam due to a lateral and axial load. When I modeled this in NASTRAN, it seemed to neglect the axial load and only calculate the deflection due to the lateral...

Yep, checked that. I was doing some more reading and am not sure if the CBUSH element is the right way to go. The way my model is setup the y-axis is the long axis of the spring. Like I said before, I want the element to have a Rz stiffness so I went ahead and created CBEAMs of but for the...

I am trying to model a torsional spring of a defined stiffness. My thought was to use the CBUSH element and define the stiffness in the Rz DOF (based on the way my model is setup). When I run the model, it is as if this restraint is ignored and the deflection is huge. Is there a better way to...

I have a question about what Beam Theory NASTRAN uses. Here are 2 simple cases that are yielding different results: Trial 1: - 2 nodes connected with a beam element - Fixed at one end, free at the other - Apply body load Trial 2: - 2 nodes connected with a beam same beam element -...

Thanks for your help everyone. After muttering over this with a couple co-workers I think we have come to a closed-form solution (quite lengthy!).