WS10-1 VND101, Workshop 10 MSC.visualNastran 4D Exercise Workbook Trebuchet

WS10-2 VND101, Workshop 10

WS10-3 VND101, Workshop 10 Objectives This exercise will introduce some of the basic features of visualNastran Desktop 4D. You will create a simple dynamic system: an ancient gravity-powered payload delivery device for warfare. It’s called a Trebuchet. The concepts emphasized with this demonstration are the: Creation and control of Constraints Body creation and positioning Modification of a simulation to vary the results.

WS10-4 VND101, Workshop 10 Exercise Overview  Open the Model  Attach Ropes  Create the Projectile  Assign Collisions  Clean the Work Area  Remove Rope Slack  Set Proper Weights  Run Simulation  Interesting Experiments and Variations

WS10-5 VND101, Workshop 10 I - Opening The Model The model has already been created in Solidworks and imported to MSC.visualNastran. 1)Open MSC.visualNastran Desktop 4D. 2)Go to File>Open to open the file Trebuchet.wm3. Trebuchet.wm3 should be in the Trebuchet folder. Figure 1 Open File

WS10-6 VND101, Workshop 10 To attach ropes from the holder to the forearm: 3)Go to View>Display Configuration...(Figure 2). A pop-up dialog box appears. (Figure 3) 4)Deactivate “Optimized mouse tracking” (Figure 3) by clicking in the box to the left of it to uncheck the option. 5)Click “OK”. 6)Right click the holder, which is the yellow half circle at the bottom of the work area, and select Visibility>Hide All Others in the pop-up menu. (Figure 4) It can also be selected under holder-1 in the Object Browser. Figure 2 View Pull-down Menu II - Attaching Ropes Figure 3 Display Configuration Figure 4 Hide All Others

WS10-7 VND101, Workshop 10 II - Attaching Ropes 7)Click once on the Box Zoom tool in the toolbar. If you move the curser around in the simulation window, you can see that it has been changed from an arrow to a magnifying glass. 8)Draw a box around the holder to zoom in on the holder. This can be done by clicking once and holding down the mouse to assign the first corner of the box, sliding the magnifying glass across the holder, and let go of the mouse button once the holder is inside the box. 9)Double-click the Coord tool. Double-clicking the coord tool will keep the tool activated. 10)Move the cursor over the edge of one of the pegs until the cursor changes to that shown in Figure 5. 11)Click the left mouse button. Use the “down arrow” on the keyboard or the Rotate Around” tool to rotate the holder to get to the third peg. Use the “up arrow” on the keyboard to rotate the holder back to it’s original view. Your simulation window should look like Figure 6 after placing a coord on each of the three pegs. 12)Click on the arrow (Select) tool in the toolbar to deselect the coord tool. Figure 5 Coord Placement Figure 6 Finished Coord Placement

WS10-8 VND101, Workshop 10 II - Attaching Ropes 13)Right-click away from any bodies in the work area and pick Show All. 14)Hit the “H” key on the keyboard to return to the “Home” view. The “Home” view can be set to a different angle by moving to that angle and pressing “S” for “Set” view. 15)Expand “arm_Assem-1” in the Object Tree Manager by clicking on the plus sign to the left of it. This expands the object or assembly to display other objects, coords, and constraints that are connected. 16)Right click “forearm-1” in the Object Tree Manager and select Visibility>Hide All Others in the pop up menu. (Figure 7) Now, all the other objects disappear except for “forearm-1”, the long, yellow, rectangular block. Figure 7 Hide All Others Figure 8 Forearm-1

WS10-9 VND101, Workshop 10 II - Attaching Ropes 17)Use the Box Zoom, and Rotate Around tools to zoom in on the end of the forearm with one hole. (Figure 8) 18)Change the model display to a wireframe by clicking the arrow next to the solid sphere in the toolbar, and then clicking the wireframe sphere from the pull-down menu. An example is shown above on the sample toolbar. 19)Use the Coord tool to place 3 coordinate systems on the model. (Figure 9) There is a coordinate system concentric with each end of the through hole and at the center of the bottom face. (Figure 9) To place the coords on the ends of the through hole, hover the mouse over the hole until the curser becomes a large circular target symbol. To place a coord on the bottom face, hover the mouse over the middle of the face until the whole face is highlighted blue. 20)Expand “holder-1” in the Object Browser. This is done by clicking on the plus symbol to the left of “holder-1”. 21)Highlight “holder-1” and its three coordinate systems. (Figure 9) To highlight all four objects, you can either hold down the “Ctrl” key and select the objects one by one, or select the holder, hold down the shift button, and select the holder and the last coordinate system. 22)Right-click within the highlighted area in the simulation window, and pick Show in the pop up menu. Figure 9 Appearance Window Figure 8 Zoom

WS10-10 VND101, Workshop 10 II - Attaching Ropes 23)Press “H” on the keyboard. Now you can see the holder and its coords. 24)Use the Box Zoom tool to zoom in on the six coordinate systems. (Figure 10) 25)Select a pair of coordinate systems shown in Figure 10. Hold down the “Ctrl” button to select multiple objects in the work area. The order in which the coords are selected do not matter. 26)Click the Create Constraint tool in the toolbar. 27)Pick “Rope” as type of constraint and click “Create”. (Figure 11) A green rope appears connecting the two constraints just highlighted. 28)Create rope constraints for the two other pairs of coordinate systems. Figure 10 Three Pairs of Coords Figure 11 Create Constraint

WS10-11 VND101, Workshop 10 II - Attaching Ropes Figure 14 Rope Tab - Center Rope 29)Select the two rope constraints connected to the through hole of the forearm and right click on one of the ropes. Use the “Ctrl” key to select both of them. It may be easier to right- click in the shaded area in the Object Browser after highlighting the two coords. 30)Pick Properties in the pop up window then click the Rope tab. (Figure 12) The Properties dialog box for both ropes appears. 31)Set the length to “17 inches”. (Figure 13) 32)With the properties dialog box still active, pick the center rope in the simulation window and set the length to 17.7 inches. (Figure 14) 33)Click “Apply” and “Close” the Properties dialog box. The ropes should now sag. (Figure 15) Figure 12 Right-Click Pull Down Menu Figure 13 Rope Tab - Two Ropes Figure 15 Sagging Ropes

WS10-12 VND101, Workshop 10 III - Creating The Projectile To create the projectile: 34)Click on the Display Settings tool in the toolbar and go to the Grid tab under Display Settings. 35)Deactivate the “Snap to Grid” option, then click “Close” to close the Settings dialog box. (Figure 16) 36)Press “Y” on the keyboard. The X, Y, and Z keys change the view such that the work area is looking along the respective axis. (Figure 17) Holding down the shift key while pressing X, Y, or Z shows the reverse view. 37)Click the Sphere tool on the sketch toolbar. 38)Click anywhere on the grid area once, move the mouse to an arbitrary diameter, and click once more to finalize the sphere. (Figure 17) The sphere will be assigned a size and location next. Figure 16 Grid Tab Figure 17 Simulation Window

WS10-13 VND101, Workshop 10 III - Creating The Projectile Figure 19 Sphere Tab 39)Double-click on the sphere just created in the simulation window. The Properties dialog box appears. 40)Click the Appearance tab. 41)Change the name to “Projectile” and click “Apply”. (Figure 18) 42)Click the Sphere tab. The Properties dialog box changes from the Appearance tab to the Sphere tab. 43)Change the radius to “1 inch”. (Figure 19) 44)Click “Close” to close the Properties dialog box. Figure 18 Appearance Tab

WS10-14 VND101, Workshop 10 III - Creating The Projectile 45)Click on the Move tool in the toolbar. 46)Click on the ball, hold the mouse, and move the ball into the holder to position the ball in the holder. (Figure 20) Once the Move tool is selected, any object can be dragged to another position. 47)Repeat the last two steps viewing from the Z-axis. (Figure 21) This is done by pressing “Z” on the keyboard and using the Move tool again. 48)Hit the “H” key to go to the “Home” view. The Projectile is now fitted into the holder, like in Figure )Click the arrow next to the wireframed sphere in the toolbar and pick the solid sphere. Figure 22 Projectile and Holder Figure 21 Z-axisFigure 20 Y-axis

WS10-15 VND101, Workshop 10 IV - Collisions To setup the collisions: 50)Right click “base-1” in the Object Tree Manager and select Show in the pop up menu. 51)Hold down the “Ctrl” key and pick “forearm-1”, “holder-1”, and “Projectile” in the Object Tree Manager. 52)Right-click on any highlighted object in the Object Tree Manager and pick Collide in the pop up menu. (Figure 23) All objects selected will now collide with each other when playing the simulation. Selecting the least amount of parts to collide reduces computing time. Figure 23 Collide 3 Objects

WS10-16 VND101, Workshop 10 V - Cleaning the Work Area To clean the work area: 53)Press “Ctrl+A” to select all of the objects and right-click on any of the object in the work area. 54)Pick Hide in the pop up menu. All the objects disappear from the simulation window. 55)De-select the objects by in the simulation window. 56)Hold down the “Ctrl” key and select the three rope constraints, “Projectile”, “pin-1”, “holder-1”, “base-1”, “forearm-1”, “BackArms-2”, BackArms- 1, and ArmSpacers-1. (Figure 24) 57)Right click on any of the highlighted objects and select “Show” in the pop up menu. (Figure 25) The simulation window should now look like Figure 26. Figure 25 Show Figure 24 Object Browser Figure 26 Simulation Window

WS10-17 VND101, Workshop 10 VI - Removing Rope Slack Having too much slack can adversely affect the projectile’s trajectory. To remove the slack: 58)Press the “Y” key to change the view. 59)Right-click “forearm-1” and pick Fixed in the pop up menu. (Figure 27) 60)Select “holder-1” and “Projectile”, then click the Move tool. You may use the shift key in the Simulation Window, but it may be easier using the control key in the Object Browser. 61)Click anywhere in the work area and drag the mouse to move the holder and projectile. Notice that the slack in the top set of ropes updated immediately. 62)Move the holder and projectile to the right to the point that there is a minimal amount of slack in the top ropes. (Figure 28) If the two are moved too far to the right, the ropes will be stretched and act like rubber bands when the simulation is run. Also, avoid lowering the holder and projectile to the point that they coincide with the base. Figure 27 Side View Figure 28 Move Holder and Projectile

WS10-18 VND101, Workshop 10 VI - Removing Rope Slack 63)Press “Ctrl+A” to select all and pick “Vel” in the Properties list that is to the lower left of the MSC.visualNastran window. (Figure 29) You may have to scroll down. 64)Enter zero for all of the velocities. (Figure 30) This ensures that everything has a initial velocity of zero. 65)Close the Properties dialog box. 66)De-select all the objects by clicking in empty space in the simulation window. Figure 29 Velocity Figure 30 Animation Frame Rate

WS10-19 VND101, Workshop 10 VI - Removing Rope Slack 67)Click the “Play” button. Because there is no velocity, the “holder-1” and “Projectile” will swing and dangle from “forearm-1” due to gravitational forces. (Figure 31) 68)Stop the simulation when it appears that the “holder-1” and “Projectile” are at rest. 69)Press “Ctrl+H” to erase the motion history. Erasing the motion history sets the current work area as the initial frame for the simulation. 70)Pick “Yes” to erase motion history. 71)Right-click “forearm-1” and select Fixed in the pop up menu to unfix the forearm. Figure 31 Running Simulation

WS10-20 VND101, Workshop 10 VII - Setting The Proper Weights The counter weight is generally 100 times heavier than the projectile. To set the weights: 72)Double-click “ArmSpacers-1” in the Object Browser and go to the Material tab. (Figure 32) 73)Set the mass to “50 lbm”. (Figure 32) 74)Repeat the last two steps for “Projectile”, but set the mass to “0.5”. (Figure 33) 75)Close the “Properties” dialog box. Figure 32 Material Tab For “Armspacers-1” Figure 33 Material Tab for “Projectile”

WS10-21 VND101, Workshop 10 VIII - Running the Simulation To run the simulation: 76)Zoom out so the ball can be seen when if flies. This can be done by clicking the Zoom Out tool, clicking the mouse in the simulation window, and moving the mouse away from you. 77)Click the “Run” button and watch the “Projectile” fly. (Figure 34) Notice that the ropes and forearm are in line when the projectile is released. This is the ideal release point. 78)Close the warning message that appears. 79)Use the “Stop” button to stop the simulation. 80)Use the “Reset” button to reset the simulation. Figure 34 Running the Simulation

WS10-22 VND101, Workshop 10 Interesting Experiments and Variations There are many variables that can be changed in this model.  Changing the length of the center rope affects the initial trajectory angle.  Changing the mass of the counter weight or projectile will affect the point at which the ropes and forearm align.  Changing the length of the main ropes also affect when the ropes and forearm align.  Select the projectile and insert a meter using Insert/Meter/Position.  Click OK in the Tiling Options window. A graph will appear where x represents how far the projectile traveled and z represents the height of the projectile.  Use the meter to see if your modifications increased the Trebuchet’s range.