In automotive engineering, ensuring that a vehicle chassis provides sufficient strength under static loads alone is not always enough to evaluate its behavior under real operating conditions. While a vehicle is in motion, the chassis is continuously subjected to varying dynamic loads caused by road irregularities, acceleration and braking, cornering maneuvers, suspension movements, and different driving conditions.
These loads can directly affect the structural behavior of the chassis, load transfer paths, forces occurring at connection points, deformation, and long-term durability.
Therefore, one of the key engineering questions in the vehicle development process is:
What dynamic loads is the chassis subjected to while the vehicle is operating under real-world conditions, and how does it behave under these loads?
To answer this question, the RecurDyn Multi-Body Dynamics (MBD) approach enables the motion of mechanical systems and the interaction forces within the system to be investigated as a function of time.
Thanks to RecurDyn's Multi Flexible Body Dynamics (MFBD) capabilities, rigid and flexible bodies can also be evaluated within the same mechanical system. This makes it possible to investigate not only vehicle motion but also structural results such as deformation, stress, and strain occurring in flexible components during operation.
The vehicle chassis is one of the fundamental structural components responsible for carrying loads transferred from the suspension, powertrain, body, and other subsystems.
Under real driving conditions, the forces acting on the chassis are not constant.
For example, when a vehicle travels over an uneven road surface, the resulting vertical wheel movement is transferred to the suspension system. Reaction forces generated by springs, dampers, bushings, and connection components are then transmitted to the vehicle chassis through connection points.
Similarly:
can generate time-dependent forces on the chassis.
Therefore, evaluating only the maximum static load applied at a specific instant may not fully represent real operating conditions in certain engineering problems.
Dynamic analysis with RecurDyn helps engineers investigate where forces originate, how they are transferred throughout the system, and how they change over time.
Multi-Body Dynamics (MBD) analysis is the time-dependent investigation of the motion and interaction forces of mechanical components connected through joints, connections, springs, dampers, contacts, and various force elements.
In a vehicle system, the model may consist of:
the chassis, wheels, suspension components, springs, dampers, bushings, connections, steering mechanism, and other mechanical components.
Rather than evaluating these components independently, analyzing them at the system level makes it possible to determine how motion or force generated in one component affects other components.
For example, the way a wheel responds to a specific road input and how this response is transferred through the suspension to the chassis connection points can be investigated as a function of time.
In MBD analyses performed with RecurDyn, both system motion and interaction forces between components can be calculated.
In a vehicle dynamics model, not every component needs to be modeled at the same level of detail. The modeling approach can be determined according to the results expected from the analysis.
For example, some components may be defined as rigid bodies, while the chassis or specific connection components whose structural deformation may significantly affect overall system behavior can be modeled as flexible bodies.
This approach enables the analysis to address not only the question:
“How does the vehicle move?”
but also:
“How do the chassis and other structural components behave while the vehicle is moving?”
RecurDyn extends the conventional rigid multi-body dynamics approach through its Multi Flexible Body Dynamics (MFBD) capabilities.
In real mechanical systems, not all components are completely rigid.
In particular:
may undergo certain levels of deformation under dynamic loads.
If these deformations have a significant effect on system motion and load transfer, the components may need to be evaluated as flexible bodies.
RecurDyn's Multi Flexible Body Dynamics (MFBD) technology enables multi-body dynamics and finite element approaches to be used within the same system.
This allows the motion of rigid bodies to be evaluated together with deformation, stress, and strain results occurring in flexible bodies.
For a vehicle chassis, this approach makes it possible to evaluate the chassis not merely as a moving rigid structure, but as a structural component capable of deforming under dynamic forces transferred through the system.
RecurDyn provides two fundamental approaches for flexible body modeling to address different engineering requirements: FFlex and RFlex.
In the FFlex approach, the nodal degrees of freedom of the flexible body are directly taken into account.
This approach can be used particularly in problems where more detailed flexible body behavior needs to be investigated. Geometrically nonlinear deformations and, with appropriate material models, material nonlinearities can also be evaluated.
The FFlex approach can also be used in flexible-body problems where contact behavior is important.
For example, if detailed investigation of local behavior caused by contact on a particular connection or structural component within a vehicle system is required, the FFlex approach can be considered.
RFlex is a reduced flexible-body approach that represents flexible-body behavior using modal information.
Particularly in large finite element models with a high number of degrees of freedom, directly including all nodal degrees of freedom in the solution can significantly increase computational cost.
By representing flexible-body behavior through selected modes, RFlex can improve computational efficiency in larger system models.
Therefore, the choice between FFlex and RFlex should be made by considering the required level of accuracy, deformation behavior, contact conditions, model size, and computational cost.
As a vehicle travels along a road, irregularities in the road surface generate motion at the wheels. This motion is transferred to the vehicle structure through the suspension system.
A simplified load transfer path can be represented as:
Road Input → Wheel → Suspension → Connection Points → Vehicle Chassis
For example, when a wheel passes over a road bump, vertical movement occurs at the wheel.
This movement generates dynamic forces in the spring and damper elements. These forces are then transferred to the chassis through suspension connection points.
The important point is that this entire process occurs as a function of time.
The maximum force, deformation, or stress on the chassis may not necessarily occur at the same instant as the maximum road input. The system's mass, inertia, damping characteristics, suspension behavior, and interactions between components can affect the results.
With RecurDyn, this dynamic system behavior can be investigated in the time domain.
The dynamic behavior of a vehicle chassis cannot be evaluated independently of the suspension system.
Within the suspension system:
can directly affect how road-induced forces are transferred to the chassis.
Therefore, one of the major advantages of the multi-body dynamics approach is the ability to investigate not only an individual component but also the interaction between mechanical subsystems.
For example, two different suspension configurations can be analyzed under the same road input, and the forces occurring at chassis connection points can be compared.
This allows the system-level effects of different design alternatives to be evaluated numerically before a physical prototype is manufactured.
Depending on the scope of the project, various engineering outputs can be evaluated through a properly developed RecurDyn vehicle dynamics model.
These may include:
By evaluating these results together, engineers can investigate not only maximum force values but also the load paths through which forces are transferred within the system.
Particularly when a flexible-body approach is used, the structural effects occurring on a specific component as a result of dynamic system behavior can be evaluated in greater detail.
In real mechanical systems, interactions between components do not always occur solely through ideal joints. In many systems, contact forces are an important part of dynamic behavior.
RecurDyn enables contact definitions to be used in models containing rigid and flexible bodies.
This capability is particularly important when analyzing mechanisms in which components come into contact with one another during motion.
By evaluating flexible-body and contact behavior within the same dynamic model, the effects of contact-generated forces on component deformation and stress behavior can be investigated.
This approach can provide significant advantages not only in automotive applications but also in rail systems, the defense industry, construction machinery, and complex mechanical system analyses.
Static and dynamic analyses are not alternatives to each other. Each analysis method addresses different engineering questions.
Static analysis focuses on evaluating structural behavior in problems where variations in loads over time and the effects of system motion can be neglected.
In dynamic analysis, however, factors associated with system motion become important, including:
Especially in continuously moving mechanical systems such as vehicles, knowing the maximum static force alone may not be sufficient.
The more important engineering question is often:
Where does the force originate, through which components is it transferred within the system, and how does it change over time?
The RecurDyn multi-body dynamics approach helps evaluate this load transfer mechanism at the system level.
In conventional component-based analyses, the loads to be applied to a specific component may need to be estimated in advance or obtained from another analysis.
However, in real mechanical systems, loads acting on individual components are often generated as a result of the motions and interactions of other components.
With system-level dynamic analysis performed using RecurDyn, these loads can be calculated directly as a result of system motion.
This approach can be used for:
identifying load transfer paths, determining critical connection points, comparing different design alternatives, evaluating suspension parameters, and investigating the dynamic behavior of flexible components.
This allows engineers to evaluate not only the strength of an individual component but also its interaction with the mechanical system in which it operates.
The primary purpose of simulation studies during the vehicle development process is not merely to generate result visualizations.
The main objective is to transform physical behavior under real operating conditions into engineering data that can support design decisions.
Through multi-body dynamics analyses performed with RecurDyn, different operating conditions and design alternatives can be compared numerically.
For example, the dynamic responses of the system can be investigated under:
The results obtained can help identify critical operating conditions and provide additional engineering data about the design before proceeding to physical prototype and testing stages.
Simulation should not be considered a process that replaces physical testing, but rather an engineering tool that supports testing and prototype development activities.
One of RecurDyn's key capabilities is its ability to combine the conventional Multi-Body Dynamics (MBD) approach with Multi Flexible Body Dynamics (MFBD) within the same analysis environment.
This enables system motion, connection forces, contact behavior, and structural responses of flexible components to be evaluated together within a mechanical system.
RecurDyn can also be used in automotive applications to investigate the dynamic behavior of systems such as complete vehicles, suspension systems, engines, and clutches under different driving and operating conditions, as well as the loads transferred to individual components.
The availability of different flexible-body approaches, such as FFlex and RFlex, also helps establish an appropriate balance between model accuracy and computational cost according to the requirements of the analysis.
Thanks to these capabilities, RecurDyn provides a powerful solution for engineering applications such as vehicle dynamics, mechanism dynamics, suspension analysis, flexible multi-body dynamics analysis, and dynamic load analysis.
At FE-TECH, we provide solutions utilizing RecurDyn multi-body dynamics analysis and engineering simulation to evaluate the behavior of complex mechanical systems under real operating conditions.
Evaluating vehicle and mechanical systems not only at the component level but also at the system level enables a more detailed investigation of the relationship between motion, load transfer, contact, and structural behavior.
By utilizing RecurDyn's MBD and MFBD capabilities, dynamic loads within the system, connection forces, and the behavior of flexible components can be evaluated during the early stages of the design process.
For your vehicle chassis dynamic analysis, suspension system analysis, RecurDyn analysis, flexible body analysis, mechanism dynamics, and multi-body dynamics analysis requirements, you can contact the FE-TECH engineering team.