Multibody Dynamics Module
Analyze Rigid- and Flexible-Body Assemblies with the Multibody Dynamics Module
Tools for Designing and Optimizing Multibody Systems
The Multibody Dynamics Module is an expansion of the Structural Mechanics Module that provides an advanced set of tools for designing and optimizing multibody structural mechanics systems using finite element analysis (FEA). The module enables you to simulate mixed systems of flexible and rigid bodies, where each body may be subjected to large rotational or translational displacements. Such analyses help identify critical points in your multibody systems, thus enabling you to perform more detailed component-level structural analyses. The Multibody Dynamics Module also gives you the freedom to analyze forces experienced by segments of the structure, and stresses generated in flexible components that may lead to failure due to large deformation or fatigue.
Utilize a Library of Joints
A library of predefined joints is included in the module so that you can easily and robustly specify the relationships between different components of a multibody system, where the components are interconnected such that only a certain type of motion is allowed between them. Joints connect two components through attachments, where one component moves independently in space while the other is constrained to follow a particular motion, depending on the joint type. The joint types in the Multibody Dynamics Module are generic to the extent that they can model any type of connection. Researchers and engineers can thereby design accurate multibody structural mechanics models, using the following joint types:
- Prismatic (3D, 2D)
- Hinge (3D, 2D)
- Cylindrical (3D)
- Screw (3D)
- Planar (3D)
- Ball (3D)
- Slot (3D)
- Reduced Slot (3D, 2D)
- Fixed Joint (2D,3D)
- Distance Joint (2D,3D)
- Universal Joint (3D)
- Orientation of movement for the prismatic, hinge, cylindrical, and screw joints.
- Orientation of movement for the planar, ball, slot, and reduced slot joints.
- The stresses in the gearbox housing and the sound pressure level in the surrounding air (top and bottom-right) of a 5-speed synchromesh gearbox inside a manual transmission vehicle. The frequency spectrum of the normal acceleration at one of the points on the gearbox is also shown (bottom-left).
- A swashplate mechanism is used to control the orientation of helicopter rotor blades. This example shows an application derived from the model where only the pitch of the blades can be changed, but where both transient and eigenfrequency analyses can be presented.
- Model of a three-cylinder reciprocating engine, having both rigid and flexible parts, is used for maximizing the engine power and the design of structural components.
- Plot of stresses in an induction motor's housing (top) and the magnetic flux density in the rotor (bottom-left). The rotor orbit at two bearing locations is also shown (bottom-right).
Complete Flexibility in Analyzing Multibodies
Components of a system that undergo deformations can be modeled as flexible, while other components, or even parts of these components, can be specified as rigid. You can also provide your multibody dynamics design and analyses with nonlinear material properties by combining models in the Multibody Dynamics Module with either the Nonlinear Structural Materials Module or the Geomechanics Module. At the same time, the rest of the physics that you can model with COMSOL Multiphysics and the suite of application-specific modules, can be coupled to the physics described by the Multibody Dynamics Module, such as the effects of heat transfer or electrical phenomena.
Transient, frequency-domain, eigenfrequency, and stationary multibody dynamics analyses can be performed. Joints can be assigned linear/torsional springs with damping properties, applied forces and moments, and prescribed motion as a function of time. Analysis and postprocessing capabilities include:
- Relative displacement/rotation between two components and their velocities
- Reaction forces and moments at a joint
- Local and global coordinate system frames of reference
- Stresses and deformations in flexible bodies
- Fatigue analysis of critical flexible bodies by combining with the Fatigue Module
Often, motion between two components is restricted due to the presence or functions of other physical objects. Limiting and conditionally locking the relative motion can be specified for the joints in order to fully define and model these complex systems. In robotics, for example, the relative motion between two arms can be defined as a pre-defined function of time. Joints can also be spring-loaded and appropriate damping factors can be included in the Multibody Dynamics Module.
Keeping Cool: SRON Develops Thermal Calibration System for Deep-Space Telescope
C. de Jonge SRON, Netherlands
Deep-space telescopes require ultrasensitive detectors and calibration to pick up weak far-infrared signals. The SpicA Far-InfraRed Instrument (SAFARI), an infrared camera that will fly aboard the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), has sensors that measure the far-infrared spectrum. The SAFARI system includes a ...
Three Cylinder Reciprocating Engine
In this example, a dynamic analysis of a three-cylinder reciprocating engine is performed to investigate stresses generated during operation, thereby permitting identification of the critical components. Demand for high power output relative to the weight of the engine requires careful design of its components. This model of a reciprocating ...
Assembly with a Hinge Joint
This example illustrates how to model a barrel hinge connecting two solid objects in an assembly. In this model, the details of the connection are not the focus of the analysis, therefore, the hinge joint is modeled using a Joint feature in the Multibody Dynamics Module. The connected parts can be either rigid or flexible or a combination as ...
Vibration in an Induction Motor
In the Vibration in an Induction Motor tutorial model, eddy currents are induced in the rotor by time-harmonic currents in the stator windings and rotation of the rotor. Induced currents in the rotor interact with the magnetic field that is produced by the coils to generate the driving torque on the rotor. The air gap between the rotor and stator ...
Dynamics of Double Pendulum
This tutorial application demonstrates the modeling of a hinge joint between two bodies in COMSOL Multiphysics. Various nodes available for joints such as Constraints, Locking, Spring, Damper, Prescribed Motion, and Friction are also demonstrated. Many real structures can be approximated with the double pendulum model. Hence a double pendulum ...
Gear Train Modeling
This model simulates vibrations in a compound gear train. Spur gears, used to model the gear train, are mounted on rigid shafts. The shafts are supported by an elastic housing at both ends. The gear mesh is assumed to be elastic with varying stiffness, which is the source of vibration. A transient analysis is performed to compute the dynamics of ...
Helical Gear Pair
This model illustrates the dynamics of helical gears. It is built using the gears functionality in the Multibody Dynamics interface in COMSOL Multiphysics. A transient study is performed to analyze the effect of constant gear mesh stiffness, varying gear mesh stiffness, and the transmission error on the angular velocity of driven gear and the ...
Helicopter Swashplate Mechanism
This model illustrates the operation of a swashplate mechanism used in helicopters to translate the input of helicopter flight control into the motion of the rotor blades, and hence controls the orientation of the rotor blades. In this model, the rotor blades are modeled as either rigid bodies or flexible bodies in two different cases. All other ...
Shift into gear
This model demonstrates the ability to simulate Multibody Dynamics in COMSOL. It comprises a multilink mechanism that is used in an antique automobile as a gearshift lever. It was created out of curiosity to find out how large forces are on the individual components. The model uses flexible parts, i.e. the Structural Mechanics Module was used ...
Spring Loaded Centrifugal Governor
A centrifugal governor is used to control the speed of rotating machinery. One of the most common applications is in controlling the RPM of an engine by regulating the fuel supply. This model illustrates the functioning of a spring loaded centrifugal governor. The dynamics of the governor are analyzed under the influence of a centrifugal force, ...
Differential Gear Mechanism
This model simulates the mechanism of a differential gear used in cars and other wheeled vehicles. A differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when a vehicle turns in order to allow the wheel that is traveling along the outside of the turning curve to roll faster and to ...