Bombas Lorentz

This example will illustrate the following concept:

• Creating “Base Node IDs” which are used to tie degrees of freedom together. In this example, Pipe Run #1 will be “slaved” to Pipe Run #2 in the Global Y direction thru Base Node ID “Spring”.

• Applying user defined loads to the piping model.

The first step is to construct the shell element model of the vessel and nozzle, where the first piping run will be attached. In this case, the vessel is 60” OD x 0.75” with a 18.0” OD x 0.375” x 20.0” long nozzle. A screen shot of the vessel input values are given below.

Once the vessel and nozzle geometry has been defined, the remaining work is to define the geometry of the attached piping runs. The following steps outline the general procedure to construct the piping model:

1. Click the “Piping Runs…” icon in the main Nozzle/PRO interface, located just above the nozzle geometry input frame.

2. Since Piping Run #1 will begin at the end of the nozzle, select the option “Start at Shell Model” and then select “End of Nozzle” from the drop down list.

3. Input the dimensions and geometry info for Piping Run #1. The inputs for Piping Run #1 are shown below. Some important features to note are:

a. To create a new row in the spreadsheet, click the “Add Row” icon in the toolbar.

b. The first pipe segment, which is the length between the nozzle and the intersection to Piping Run

#2, has an “End Label” defined at the end of the pipe segment. This End Label is defined as

“Spring1”, which will be the same name assigned to the Base Node ID in Piping Run #2.

Therefore, by defining “Spring1”, the pipe segment will be slaved to Piping Run #2 thru Base Node ID “Spring1”.

Input for Piping Run #1

4. After completing all the input for Piping Run #1, click the “Create New Piping Run” button to create a new input tab sheet for Piping Run #2. This should add a new tab to the tab list with title “Pipe #2”.

5. Piping Run #2 will begin from the top of the shell model. Therefore, the appropriate selection for the start location is “Start at Shell Model” with the location designated as “Top of Parent”.

6. Next, input the piping geometry for Piping Run #2. The input spreadsheet should be as shown below for Piping Run #2 (see image of input screen below for additional guidance):

a. Important – In Row #2, the Global Y restraint with the Base Node ID which ties Piping Run #2 and Piping Run #1 together must be defined. To do this, follow these steps:

i. Open the Piping Restraints screen selecting the cell in Row #2 within the “Restraints”

column, then click the blinking arrow button.

ii. When the Piping Restraints screen appears, click “Add Row” to generate a new restraint for the pipe segment.

iii. Since the restraint should act in the Global Y direction only, select “Global Y” from the Restraint Type column.

iv. The spring which is being simulated will have a linear stiffness of 1.0e5 lbf/inch. Specify this value in the Stiffness input column.

v. Specify the Base Node ID which is used to uniquely identify this Base Node. In this example, the Base Node ID is “Spring1”. Recall that this same variable name was used as the End Label within Piping Run #1. Now that the Base Node ID and restraint is created, Piping Run #1 and Piping Run #2 are tied together by the user defined stiffness in the Global Y direction.

vi. Click OK to return to the main piping input form.

Piping Input for Piping Run #2

Piping Restrain Input for Piping Run #2, Row #2

7. To illustrate the way in which the degrees of freedom will be tied together between Piping Run #1 and #2, the user can apply two directional loads to the free end of Piping Run #2. One load will be in the Global Y direction and one load in the Global Z direction. To define these end loads, use the following steps:

a. In Row #3, the last input segment for Piping Run #2, click on the cell within the column End Forces, then click the blinking arrow button .

b. When the Piping Loads screen appears, specify 10,000 lbf in the weight case for the Global Y and Global Z directions, in the Weight and Operating load cases.

c. Click OK to return to the main piping input form.

Piping Restrain Input for Piping Run #2, Row #3

8. All of the input should now be complete. Next, click the RUN FE button in the main Nozzle/PRO interface screen to run the analysis. The results should indicate that only the Global Y degree of freedom has been linked between Piping Run #1 and #2.

a. Since only the Global Y direction degree of freedom is tied between Piping Run #1 and #2, there should only be displacement in the Global Y direction for Piping Run #1. There should be no displacement in the Global Z direction (other than a very small amount translated thru the shell model due to torsion loading of the shell model by Piping Run #2).

b. Results from the FEA are shown below. Global Y displacements are shown in the figure at left.

As expected, the Base Node has tied the Global Y degree of freedom between Piping Run #1 and

#2, resulting in Y displacements. Since the Base Node has only linked the Global Y displacement, there are no other displacements translated through the base node tie. Therefore, even though a Z direction load is applied to Piping Run #2, it is not translated to Piping Run #1 as shown in the right-hand figure.

Left – Global Y displacement showing affect of Base Node. Loads are transferred in Global Y direction.

Right – Global Z displacement. Note that Base Node did not transmit Global Z loads or displacements.

Chapter 5 – Section 3