92 - creating a pressure load with spatial variation – exercise.pdf

7/27/2019 92 - Creating a pressure Load with Spatial Variation Exercise.pdf

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StructuralLoadsCreatingapressureLoadwithSpatialVariationExercise

Exercise: Creating a Pressure Load with Spatial Variation

Objectives

After successfully completing this exercise, you will be able to:

Understand how a pressure load is applied. Apply equations from engineering theory (Hydrostatic Pressure) and determine how

to introduce them into Mechanica.

Understand how to apply a load as a function of coordinates.ScenarioThere are several situations in which the load applied is uniform and does not change over

the surface or edge it is applied on. In addition, Force/Moment loads always maintain aconstant direction with respect to the selected coordinate system.

However, there are several applications in which the load must remain normal to the

surface it is applied on. Pressure is a force per unit area created by fluids and will alwaysact normal to the surface they are applied on. In some cases, such as a propane tank orscuba tank, the pressure is more or less constant across all the interior surfaces. On the

other hand, anyone who has been diving knows that pressure increases the deeper you

descend. For this exercise, you will apply a pressure load to a water tank to simulate

Hydrostatic pressure.

HydroLoad water_tank.prt

Task 1. Open the Mechanica application and Measure Tank Height.

1. Click Applications > Mechanica > OK.

2. Click Analysis > Measure > Distance. Select the top surface of the tank and the

PRT_CSYS_DEF as shown in the figure. The distance should be reported as 4.1.

Click Accept .


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Task 2. Determine the equation to be applied and apply the pressure load.

The hydrostatic pressure in the tank will be equal to zero gauge pressure atthe waters free surface, so the distance or height of that surface with

respect to the coordinate system has to be measured. The equation of

hydrostatic pressure is p=gh. The density of water is 1000 kg/m3, theacceleration of gravity is 9.81 m/s2. The depth h is the depth from the freesurface of the tank. If 4.1m is the distance to the free surface, then the


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depth of the water in any point in the tank is given by the expression (4.1

y). The equation governing the hydrostatic pressure then becomesp=(1000)(9.81)(4.1y).

1. Click Pressure Load from the Mechanica toolbar.

2. Select the inner surface of the tank as shown in the figure for the load

application.

3. Click Advanced and select Function of Coordinates from the Spatial Variationdrop-down menu.

4. Type 1.0 for the pressure. The dialog should appear as shown in the figure.

Because you entered 1.0 for pressure, this will act as a scaling factor for thevalues that will be returned from the function.


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5. Click Function in the Pressure Load dialog box. Click New, verify that the

Definition field is set to symbolic and type 1000*9.81*(4.1-y) in the field.


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6. Click Review , type 3.1 for the Lower Limit, 4.1 for the Upper Limit, and click

Graph.

7. Click File > Exit to close the Graphtool. Click Done > OK > OK to return to the

Pressure Load dialog box.

8. Click Preview to view the pressure distribution on the tank.

9. Click OK.

Task 3. Save the model and erase it from memory.

1. Return to the Standard Pro/ENGINEER mode by clicking Applications > Standard.

2. Click Save from the main toolbar and click OK to save the model.

3. Click File > Erase > Current > Yes to erase the model from memory.


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This completes the exercise.

92 - creating a pressure load with spatial variation – exercise.pdf

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