How to Construct and Analyze a Cylindrical tank in Autodesk

PART I: Creating your tank 1) Open Autodesk Inventor Fusion 2013 2) Click “New” 3) Home Sketch New Sketch Select XY plane 4) Sketch Center-Radius CircleSelect (0, 0) as your center point enter outer radius of tank

click enter until circle changes color

5) Select the circle. Make sure to click inside the perimeter of the circle instead of selecting the

edge. 6) An extrude icon will pop up. Select extrude. Enter inside height of tank. Double click “Enter”

7) SketchCenter-Radius CircleSelect the middle of the top of the tank as the center-->Enter in

the inner radius of your tankClick “Enter” twice

8) Select the inside circleextrude enter the negative value of your tank’s height to cut through

9) SketchCenter-Radius Circle Drag mouse to the upper rim of the tank and hold shift to lock

sketch planeSelect the center point as the center of circledrag radius until it locks with the outer edge”Esc”

10) Hold down shift and select both the inner and outer circlesextrudeenter thickness for your roof slab”Enter” 2xrepeat for the bottom of the tank

At this point you should have a hollow, symmetrical cylinder that you cannot see the inside of. Save the part and Select Simulation Mechanical in the Home tab. This will open Autodesk Multiphysics, allowing you to stress and analyze your tank.

PART II: Loading your Tank 1) Once Multiphysics opens, it will prompt you to choose analysis type. Select the default

“Static Stress with Linear Material Models” 2) In the FEA editor column on the left of the screen, right click “Element Type” under “Part 1”

and select “Brick”. Edit “Element Definition” Midside NodesIncludedOK

3) Right Click “Material” ConcreteSelect the concrete strength you prefer or alter its

conditions 4) Go to the “Mesh” tab3D Mesh SettingsMesh Type= SolidMesh Size= approximately

70%Mesh Model

5) In the left panel, expand the surfaces tab and make invisible the outside of the tank by

holding control and selecting surfaces 1,2,4,5,6, right-clicking and unchecking visibility. This should leave just the inside of the tank visible.

6) Select the inside surface of the tankRight ClickAddSurface hydrostatic Pressure

7) Enter the fluid density of water (62.4 lbf/ft^3), Select the Z button in “Fluid Depth Direction

(V)”, and enter the coordinates of the point that would lie on the top of the water in your tank. For this tutorial we used X=0, Y=inner radius of tank, Z=height of tank. Select “OK”

8) Make the rest of the surfaces visible again

9) Constrain the bottom surface by selecting the bottom surfaceRight ClickAddSurface General Constraint-->Fixed

10) To add rebar, complete the following steps 11) Select DrawLineUnclick “Use as Construction” Select the location on the mesh where

you would like to add the rebar (The maximum hoop stress in a tank occurs approximately 1/4-1/3 up the height of the tank. This is the best place to reinforce with rebar).

12) Unfortunately, the only way the lock the rebar into place while still staying attached to the tank is to manually select each vertex in a horizontal line all the way around the tank. If you skip nodes, the rebar won’t lock itself to the tank there, causing irregularities in geometry and adding stress concentration.

13) Once you’ve created a line circling the tank, edit its properties in the left columnPart 2Element Type = BeamElement Definition=Inertial Properties of your RebarMaterial=Edit values for your rebar You may add as many bars of rebar as you want. For the purpose of this tutorial we will only use one though.

PART 3: Analyzing your tank Your tank simulation is now ready to run. But first go to setup GravitySet for standard gravityOK Select AnalysisRun Simulation *The more refined your mesh size is, the longer it’ll take for Autodesk to simulation your tank. With the mesh size of 70% we picked before, Autodesk should only take about a 1:30 It may be useful to add a slice plane to examine the inside of your tank Select Results OptionsSlice planesAdd Slice planeYZ plane You can also fool around with how the tank visually appears by going to ViewVisual Style Personally I prefer shaded with mesh.

At this point it’s up to you how you would like to analyze your tank. It’s important to note that while normally, Von Mises is a good determination of maximum stress in your part, it is not useful here because of stress concentration at corners and connection points. Hoop stress is what you’re most concerned about in tanks. Either the YY or XX tensors will give a good approximation of hoop stress. To find the stress the rebar alone undergoes, select the “Beams and Trusses” option in Result Contours

It might also help to change the units to inches. Thus stress will appear in psi. For this tutorial, the tank undergoes a maximum tensile stress of 3.5 psi and a maximum compressive stress of 12 psi. Considering the yielding stress of concrete is over 100 psi, it is reasonable to conclude that this tank will not come close to fracturing due to the hydrostatic loading from the water it contains. This tutorial was created by: Engineers Without Borders Lehigh University Chapter Project Class, Tank Group, Fall 2012 For questions contact: Zachary Pelli B.S. Mechanical Engineering 2014 Lehigh University 203-223-4067