Multibody Dynamics Module
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)
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.
Multibody Dynamics Module
- Joints can be constrained to restrict the relative motion between the two connected components
- Joints can be locked to freeze the relative motion between the two connected components at the specified value
- Spring conditions can be applied on the relative motion at a joint, either at the equilibrium or with pre-deformation
- Lumped mechanical systems can be built, and can consist of masses, dampers, springs, and more
- Damping or dashpot conditions can be defined to specify losses on the relative motion at a joint
- Joints can be required to prescribe the relative motion between the connected components
- Frictional loss to a joint can be added for the joint types: Prismatic, Hinge, Cylindrical, Screw, Planar, and Ball.
- Cam-Follower condition
- Forces and moments can be applied to all types of joints at the attachments to the components
- Mechanisms can be initialized to translate and rotate rigidly with the given velocities about the specified center of rotation
- Part Library with parametric geometry parts for internal gears, external gears, and racks
- Engine dynamics
- Biomedical instruments
- Vehicle dynamics
- General dynamic simulations of mechanical assemblies
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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 ...
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 ...
Modeling 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 ...
Dynamic Behavior of a Spring Loaded Rotating Slider
This model illustrates the modeling of slider motion caused by a base rotation. The motion of the slider is analyzed under various forces such as inertia force, centrifugal force, spring force and damping force. The prismatic joint, which is used to connect the two components, is spring loaded and also includes damping effects. The motion of ...
Modeling of 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 ...
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 ...
Stresses and Heat Generation in Landing Gear
This model simulates the dynamics of the shock absorber used in a landing gear mechanism of an aircraft. It analyses the stresses, as well as the heat generated in the landing gear components due to the energy dissipated in the shock absorber. A prismatic joint, with spring and damper, is used to model the shock absorber assembly.
Modeling Gyroscopic Effect
Gyroscopes are used for measuring the orientation or maintaining the stability of airplanes, spacecraft, and submarines vehicles in general. They are also used as sensors in inertial guidance systems. This model demonstrates the modeling of a mechanical gyroscope. It analyzes the response of the spinning disc to an external torque coming on the ...
Dynamics of Helical Gears
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 ...
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