Create and Test NLFE Helical Springs

A helical spring, or a coil spring, is a member that stores energy and subsequently releases it. A helical spring is used in various applications like: automobile suspensions, engine valves, measuring scales, box springs, etc. An NLFE helical spring system is a MotionView system definition that can be used to represent a spring as a non-linear finite element body.

A helical spring needs the following entities to be present in the model:
  • Body 1 attachment - The body to which the spring will be attached at one end.
  • Body 2 attachment - The body to which the spring will be attached at the other end.
  • Point 1 attachment - Spring center point at the Body 1 attachment end which will be used to interface the spring with Body 1 attachment.
  • Point 2 attachment - Spring center point at the Body 2 attachment that will be used to interface the spring with Body 2 attachment.
  1. From the Subsystems toolbar, click the NLFE Helical Spring Subsystem toolbar icon .
    The Add an NLFEHelicalSpring Subsystem dialog is displayed.
  2. Click the System collector and decide which system the spring needs to be created in.
  3. Specify a variable name and label for the spring.
    By default, variable names of entities in MotionView follow a certain convention. For example, all NLFE helical spring entities have a variable name starting with nlfehs_. This is the recommended convention to follow when building models in MotionView since it has many advantages in model editing and model manipulation.
  4. Double-click the MaterialProperty collector and select a material to define the spring, or accept Steel as the default.
  5. Click the Body 1 collector and select the attaching body at end 1 from the modeling window, or double-click the collector to display the Model Tree (from which the desired body can be selected).
  6. In the same manner, use the Point 1 collector to select the attaching point at end 1 corresponding to Body 1.
  7. Select the attaching body at end 2 and the corresponding point with the Body 2 and Point 2 collectors.
  8. Enter values for Wire diameter, Spring diameter, Num of active coils, and Num of inactive coils.
  9. Click OK.
    The helical spring system that is created has the following architecture:
    Entity Description
    Body A large deformation entity for the spring is created.
    DataSet A dataset where editable values are populated. After the creation of the helical spring, you can change the parameters like spring diameter and wire diameter from this dataset.
    Markers A bottom and a top marker are created at the spring centers.
    Points The points that define the spring profile are defined in the cylindrical coordinates system with respect to the marker at the spring bottom. The point and hence the entire spring position and orientations are governed by this marker.
    Template The helical spring that is created has coil-to-coil contact elements. This contact is modeled using a NLFE spring-damper entity called a LINE2 element. These elements are not supported in MotionView and hence are added in the form of a template.
  • Activate Show additional parameters to specify variable names and labels for the points that are to be created. You can also edit the element density per coil of the spring coils.
  • To return to default settings, click Reset to Defaults.

Test a Helical Spring

A test rig can be used to exercise a helical spring and plot its characteristics.

A test rig for a helical spring is provided in the installation at <altair_install>/utility/mbd/nlfe.

  1. Load the test rig model MDL file testrig_helicalspring.mdl in MotionView.
  2. This model contains two bodies at two different ends. Each end contains a point Spring cap1 pt and Spring cap2 pt. Position these points such that they represent the ends of the springs that need to be tested.
  3. Build the NLFE helical spring using the Subsystems tool, as described in the earlier section.
  4. Save the model with a different file name.
  5. The model contains an event that imparts a sinusoidal excitation of 10 units in 1 time unit. Solve the model using the Solve tool.
  6. From Analysis menu, click Reports.
  7. The NLFE Coil spring test report should be available as an entry. Select it and click OK.
    A page is added to the session that contains an animation window and a plot window. The plot shows the helical spring stiffness.