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# Longitudinal Forces in Horizontal Vessel

## Longitudinal Forces in Horizontal Vessel

(OP)
I'm designing a vessel in Compress that will be mounted on a trailer and pulled behind a truck. Therefore, I'm trying to minimize weight and material where possible to keep the trailer loading down.

The vessel itself is very light, <5000lbs, so the saddles it will be mounted on don't require a lot of strength as far as the vessel is concerned. I'm trying to account for road conditions, in particular an emergency stop of the tow vehicle.

I have attempted to add loads, but I don't see how I can focus a load down the centerline of the vessel. I can apply an additional load perpendicular to the shell, but not along the centerline.

A quick read through these forums seems to imply the best way to go about this is to develop a wind load that would be comparable to the force exerted when braking. I had also considered replacing the force term in the "secondary bending and axial stress in the saddle..." with the force I would expect to see acting on the vessel under braking, essentially replacing the force exerted by friction under the saddle feet under thermal growth with the braking force of the truck.

Is there a better way to go about this or will one of my above mentioned plans work?

### RE: Longitudinal Forces in Horizontal Vessel

That is a tricky problem, but I think one of your plans will work. You will have to do alot of checking to make sure that what you do in Compress is calculated similar to how it would be done by hand. You might lose a piece here or there when Compress calculates the various load cases.

Also, make sure that axial stress in the saddle is the same direction as the vessel.

Another approach would be to do it by hand. Compress has given you all the equations and checks that you would make for a similar calculation. All you have to do is follow the same script for this particular load case. Then include it as an appendix in your calcs. I have done that many times for vessels with some special loading involved.

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