Multibody Dynamics Module Updates

For users of the Multibody Dynamics Module, COMSOL Multiphysics® version 5.3a brings a new physics interface for modeling lumped mechanical systems and a new Cam-Follower joint type. Learn about these multibody dynamics features below.

Lumped Mechanical System Physics Interface

With the new Lumped Mechanical System physics interface, you can model discrete mechanical systems in a nongraphical format, in terms of masses, dampers, springs, and more. This is particularly useful for creating equivalent circuit models in electromechanical systems like loudspeakers. The interface can be added to components of any dimension from 0D to 3D, and lumped components can be connected to finite element models in any dimension.

A demonstration of the Lumped Mechanical System interface in the Multibody Dynamics Module.

The available features in the Lumped Mechanical System interface.

The available features in the Lumped Mechanical System interface.

Cam-Follower Joint

The new Cam-Follower joint in the Multibody Dynamics interface is used for modeling a situation where a point on one object follows the boundary of another object. This new functionality makes it much easier than before to model cam shafts and similar mechanisms. The cam and follower parts can be either rigid or flexible. As a result, with this feature, you can also obtain the contact force between the two parts.

A model geometry with the Cam-Follower joint, new with version 5.3a of the COMSOL software.

A cam-follower mechanism modeled with the new joint of the same name.

A cam-follower mechanism modeled with the new joint of the same name.

Improved Default Plots

The default plots in the structural mechanics physics interfaces have been updated to produce more informative visualizations. The Application Library tutorials have been updated accordingly. Some of the more prominent changes that you will see are as follows:

  • The color table for von Mises stress plots is RainbowLight
  • The color table for mode shape plots, for eigenfrequency and linear buckling studies, is AuroraBorealis
  • Mode shape plots have the legend switched off to emphasize that the amplitude of a mode does not have a physical meaning
  • The color table for section force plots in the Beam and Truss interfaces is Wave, with a symmetric color range
    • This makes it possible to immediately distinguish between tension and compression, for example
  • In contact analysis, a plot of the contact pressure is added, as either a line plot (2D) or contour plot (3D)
  • The default plot for Stress Linearization now has a legend for the graphs
  • The default Undeformed geometry plot, produced by the Shell interface, has new colors
  • When a material model like plasticity or creep is used, a contour plot of a relevant strain quantity, like the effective plastic strain, overlays the stress plot
    • Applicable for the Nonlinear Structural Materials Module and the Geomechanics Module
  • In the Fatigue interface, the Traffic color table is used for predicted cycles to failure and for usage factors
    • Applicable for the Fatigue Module
A visual comparison of the improved default plot in COMSOL Multiphysics version 5.3a and an older software version.

In this example, you can see brighter colors in the stress plot (RainbowLight color table), and plastic strain contours and contact pressure contours have been added by default. For comparison, a plot from the default plot in COMSOL Multiphysics® version 5.3 of the same model is shown.

In this example, you can see brighter colors in the stress plot (RainbowLight color table), and plastic strain contours and contact pressure contours have been added by default. For comparison, a plot from the default plot in COMSOL Multiphysics® version 5.3 of the same model is shown.

New Tutorial Model: Modeling a Radial Cam-Based Valve-Opening Mechanism

In this tutorial model, you can study a spring-loaded valve-opening mechanism that has a rocker arm and a radial cam. All of the system components are modeled as rigid and are connected through prismatic, hinge, and slot joints, as well as the new cam-follower joint. A transient analysis is performed for various spring stiffness values. The output from the model includes, among other things, the follower velocity, follower acceleration, cam-follower connection force, and the required torque.

Visualization results of a radial cam-based valve-opening mechanism model.

The surface plot shows the vertical velocity and the arrows show the velocity field in the component. In the graph, the acceleration history of the follower is shown.

The surface plot shows the vertical velocity and the arrows show the velocity field in the component. In the graph, the acceleration history of the follower is shown.

Application Library path:
Multibody_Dynamics_Module/Tutorials/radial_cam_follower

New Tutorial Model: Lumped Model of a Vehicle Suspension System

In this tutorial, a vehicle suspension system having 11 degrees of freedom is analyzed with a lumped model. The Mass, Spring, and Damper nodes of the Lumped Mechanical System interface are used to model the wheels, including suspension system, as well as the seats with a passenger. The vehicle body, having 3 degrees of freedom, is modeled as a rigid body in the Multibody Dynamics interface. A transient analysis is performed to compute the vehicle motion and the seat vibration levels for a given road profile.

A collage from the Lumped Model of a Vehicle Suspension System tutorial model.

The conceptual model of the car body shows the wheels and seats (background), modeled through the corresponding nodes in the Lumped Mechanical System interface (transparent), to calculate the accelerations in the four seats (foreground).

The conceptual model of the car body shows the wheels and seats (background), modeled through the corresponding nodes in the Lumped Mechanical System interface (transparent), to calculate the accelerations in the four seats (foreground).

Application Library path:
Multibody_Dynamics_Module/Automotive_and_Aerospace/lumped_vehicle_suspension_system

New Tutorial Model: Lumped Model of a Human Body

In this model, you can analyze a lumped model of a human body with 5 degrees of freedom. The Mass, Spring, and Damper nodes of the Lumped Mechanical System interface are used to model the human body and the shoe-ground interface. First, an eigenfrequency study is performed to find out the natural frequencies of the system. Then, a frequency response analysis is performed to compute the system response for a specified base excitation.

A transmissibility plot from the Lumped Model of a Human Body tutorial.

Transmissibility of vibrations from the ground to the lower body for three different soil stiffness values.

Transmissibility of vibrations from the ground to the lower body for three different soil stiffness values.

Application Library path:
Multibody_Dynamics_Module/Biomechanics/lumped_human_body

Updated Tutorial Model: Lumped Loudspeaker Driver Using Lumped Mechanical System

This is a model of a moving-coil loudspeaker where a lumped parameter analogy represents the behavior of the electrical and mechanical speaker components. The Thiele-Small parameters (small-signal parameters) serve as input to the lumped model. In this model, the mechanical speaker components such as moving mass, suspension compliance, and suspension mechanical losses are modeled using the Lumped Mechanical System interface.

A plot from the Lumped Loudspeaker Driver tutorial model.

Pressure field plotted as isosurfaces (above the speaker cone) and as a surface plot (below the speaker cone).

Pressure field plotted as isosurfaces (above the speaker cone) and as a surface plot (below the speaker cone).

Application Library path:
Acoustics_Module/Electroacoustic_Transducers/lumped_loudspeaker_driver_mechanical