Defining constraints

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In this video, you’ll

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convert an analysis diagram into structural constraints,

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convert a written description of structural constraints,

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apply structural constraints accurately,

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differentiate structural constraints and loads,

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apply frictionless constraints to symmetry models,

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and, explain limitations of structural constraints.

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To execute a static simulation study, you need to prevent all rigid body motion,

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such as free translational and rotational movement

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that can occur in response to applied loads.

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This process is known as making the model statically stable.

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To do that, you must either apply a fixed constraint to a face,

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or combine partial constraints on faces, edges, or vertices.

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Loads and constraints often replace unnecessary parts that do not need to be modeled.

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For example, you may want to know if your shelf can withstand the weight of objects.

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You can use a constraint to replace the wall that it is attached to.

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Constraints define where and how the model is fixed.

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To begin, open the analysis diagram Defining Constraints.PNG.

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At the upper left, a pinned constraint is to be applied

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to the hole of the arm that will allow the model to rotate.

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At the lower left, two fixed constraints are to be applied to fix the flat faces in space.

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The right side of the part requires an enforced displacement

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of 0.1mm in X to be applied to the holes, forcing them to move 0.1mm in the X direction.

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Once you have reviewed the analysis diagram, in Fusion 360, open the file Defining Constraints.f3d.

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On the Toolbar, navigate to the Simulation workspace.

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From the Toolbar, expand Constraints and select Structural Constraints.

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This displays the Structural Constraints dialog.

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The first constraint to apply is the pin constraint to the hole of the arm.

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Pin constraints prevent movement in radial, axial,

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and tangential directions and are only applicable to cylindrical surfaces.

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In the dialog, expand the Type drop-down and select Pin.

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Then, in the canvas, select the upper-left hole.

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Back in the dialog, ensure that both the Radial and Axial directions are selected.

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With Radial selected, nodes along the cylindrical surfaces cannot move or deform radially.

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With Axial selected, nodes along the cylindrical surfaces cannot move in the axial (thrust) direction.

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Leave the Tangential direction deselected.

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When Tangential is selected, nodes along the cylindrical surface

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cannot translate in the tangential direction, which prevents rotation of the cylinder around its own axis.

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As it is deselected, the part will be allowed to rotate about the pin.

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Click OK.

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Now, apply a fixed constraint.

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From the Toolbar, expand Constraints and select Structural Constraints.

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In the dialog, ensure that the Type is set to Fixed.

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In its default setup, the fixed constraint prevents all movement or deformation

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on the selected entity by constraining all 3 translational degrees of freedom.

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A fully constrained model eliminates rigid body movement.

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In the canvas, orbit and zoom the part to better view the lower-left arm.

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Select both faces of the corner.

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Back in the dialog, make sure that Axis has all three directions selected

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so that all directions are fixed, and so the faces are prevented from moving.

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Click OK.

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Finally, apply a prescribed displacement constraint on both holes on the right arms.

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Again, open the Structural Constraints dialog and set the Type to Prescribed Displacement.

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A Prescribed Displacement constraint is used when you do not know the size of the load,

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but you know how far the object should deflect.

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In the canvas, select both holes.

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Then, in the dialog, prescribe the magnitude of displacement using vector specifications.

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In the Ux field, enter 0.1.

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Click OK.

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With the constraints placed, from the Toolbar, Solve panel, click Solve.

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The Solve dialog displays.

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Select Solve.

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A Job Status dialog appears, indicating the progress of the study.

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Close the dialog.

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When it is finished, the canvas updates with results of the constraints.

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Save the model.

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Next, open the file Defining Symmetry Constraints.PNG.

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In this example, frictionless constraints will be applied

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to mimic the symmetry of a model to reduce computational time.

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A frictionless constraint prevents every point on the face from moving or deforming

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in the directions normal to the face.

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The face is free to rotate, move, or deform in the tangential directions.

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In the diagram, there is a cylinder with a fixed constraint applied to the base

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and a 100N load applied uniformly to the top surface.

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Because it is symmetrical at its axis, you can simplify the model into a quarter

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and apply frictionless constraints to the two cut surfaces to expedite the computation.

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In Fusion 360, open the file Defining Symmetry Constraints.f3d.

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From the Toolbar, navigate to the Simulation workspace.

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The cylinder in this simulation model has already been simplified.

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Now, you must modify the force used.

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In the Browser, under Load Case1, under Loads, select Force1.

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The load displays in the canvas.

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Next to Force1, select Edit.

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This displays the Edit Structural Load dialog.

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In the Magnitude field, replace the 100N force with 25N.

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This is a quarter of the original load because only a quarter of the model is being used.

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Click OK.

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Now it is time to place frictionless constraints on the two cut faces.

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From the Toolbar, expand Constraints and select Structural Constraints.

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In the Structural Constraints dialog, expand the Type drop-down and select Frictionless.

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Then, in the canvas, select one of the cut faces.

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Click OK.

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Repeat this process, opening the Structural Constraints dialog,

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setting the Type to Frictionless, and then, in the canvas, selecting the other cut face.

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Now, solve the study.

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From the Toolbar, Solve panel, click Solve.

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In the Solve dialog, select Solve.

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The Job Status dialog displays, indicating the progress of study.

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Close the dialog.

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When it is finished, the results display in the canvas.

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Save the model.

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Finally, it is possible to specify bolted connections within the Simulation workspace.

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Open the file Bolted Connection and Separation Constraint.f3d.

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Then, from the Toolbar, expand Constraints and select Bolt Connector.

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The Bolt Connector dialog displays.

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A bolt connector adds an idealized bolt to your simulation study without you having to model it.

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You can choose a bolt that uses either a threaded hole or a nut to fasten the connection.

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In the canvas, select the location of the bolt head, which is the upper circular edge.

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Then, orbit the model and select the lower circular edge.

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The bolt connector displays.

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In the dialog, you can specify whether a Head Washer is used by enabling the checkbox next to Head Washer.

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The canvas updates.

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Enable Nut Washer.

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Again, the canvas updates.

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Under Preload, in the Preload Value field, enter 3000 N.

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Under Material, you can modify the material being used by the bolt.

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For now, leave the material set as-is.

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Click OK.

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Orbit the model to review the bolted connection.

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Save the model