Try it: Setting up an initial clash test in Navisworks. 

1. In Navisworks Manage , open the Navisworks File Set SMALL_HOSPITAL_COMBINED-Clash.nwf.   
2. In the Home tab > Select & Search panel> click Selection Tree. You can see that this file set has three models linked in:
   56750_A.nwc – architectural and site content
   56750_M_Systems.nwc – mechanical, electrical, and Plumbing content
   56750_S.nwc – structural content
3. We are going to start our investigation by checking clashes between Structural Beams and Mechanical Pipes. Since we do not need to see the architectural model for this test, in the Selection Tree, right-click on the architectural model and select Hide.
4. In the Home tab > Tools panel, click Clash Detective.
5. In the Clash Detective window, in the upper right corner, click Add Test.
6. In the Name edit box, type in a name that matches the clash you want to run. In this case, Structural Beams and Plumbing Piping.
7. In the Rules tab, review the existing rules that come with the software. These rules instruct the program to ignore clashes between typical issue that are not important in your clash. You can also create new rules.
8. Now you are ready to define what you see in the clash. In the Select tab, in the Selection A panel, expand 56750_S.nwc (the structural model). Select Structural Framing. The on-off toggle buttons allow you to select from Surfaces (the most likely), as well as lines, points, and self-intersecting geometry.  You can also use a current selection on the screen or select items on the screen if you want to only run a clash in a specific part of the models.
9. In the Section B panel, expand 56750_M_Systems.nwc and select Pipe Fittings , hold down the Ctrl key and select Pipes.
10. In the Settings panel, you can set the type of clash: Hard – where two objects actually intersect, Hard (Conservative) where two objects are very close , Clearance – where two objects come within a specific distance – for example you may want to have space around objects for insulation, and Duplicate – where the two items are the exact same type and position. In this case we will run a Clearance clash using the default tolerance.
11. Link – to TimeLiner or animation.
12. Click Run Test.
13. When the test is completed the Results tab automatically opens. In this example we have 20 clashes. (CHECK THIS). 
14. Let’s review  a few of these clashes. Move or resize the Clash Detective window so you can see the model. Click on one of the clashes and it automatically zooms in on the part of the model. The main part of the model is changed to wireframe so the clashes stand out.
15. Click through several clashes.
16. In the Clash Detective, in the Display Settings area, you can modify how clashes are highlighted and Isolated as well as set the viewpoint – Auto-update automatically zooms in on the clash.